PYRAMID Rebuild & Machine, LLC
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"Make It Last"
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Articles
• Not only are we proud of our work, we're confident in the knowledge that backs it up, and we're not shy about sharing our know-how, either. Below you'll find articles on rebuilding, retrofitting and repairing machine tools. They were written by Jim Leigh, a co-owner of Pyramid, who has more than two decades of experience in this business. He also is named on U.S. and foreign patents and has served as an expert witness on machine condition and repair.
We hope you'll find these articles helpful. In reading them, if you have any questions or comments, please let us know. (All the material below is copyrighted by Pyramid Rebuild & Machine LLC.)
Proper tailstock alignment is vital
Having a premium lube system pays off
A simple way to check machine tool geometry
Tips on trouble-free machine tool installation
When done right, machine-tool retrofit can save thousands
How to prevent accuracy from slipping away
Ten tips to make your machine tools last
Finding run-out cause takes detective work
Proper tailstock alignment is vital by Jim Leigh, Pyramid Rebuild & Machine co-owner
When operators are having difficulty maintaining consistency on turned or ground work-pieces, a culprit that's often overlooked is the machine's tailstock. A misaligned tailstock can cause taper, inconsistent size, oversize holes, out of square shoulders and a lot of frustration for you and your operators.
On both lathes and grinders, the tailstock must be concentric with the work-piece spindle and parallel to the bed ways in two planes simultaneously. In addition, the guide surfaces on the tailstock base must fit properly on the bed's guide ways, which must be straight and true to the spindle.
Make sure the tailstock quill fits properly within the housing. A loose-fitting quill will cause the same problems as ill-fitting ways.
Before checking the tailstock's alignment, make sure the machine bed is level, and if you're checking a grinder, make sure the sub-table is set parallel to the bed. Next, clamp the tailstock down, extend the quill and lock it.
Mount an indicator on the cross-slide of a lathe or to the wheel-head of a grinder. Set a zero with the indicator needle touching the top of the quill. Now move the slide and read the indicator along the length of the quill. Record the measurement and take a reading on the side of the quill. On a lathe the readings should be within .001 inches per foot.
On a grinder they should be half of that. If they aren’t, you have an alignment problem. If you find that you must always adjust the tailstock from side to side every time you move it, it's because the tailstock is not true to the bed-ways.
Now turn or grind a piece between centers in the machine. If you have a pre-ground mandrel with centers in it, you can use that instead.
With the mandrel or test piece mounted between centers, run an indicator along the top of it. As earlier described, the indicator should be mounted to the cross-slide on a lathe or to the wheel-head of a grinder. Record the error. Assuming the piece you are checking is straight, the error should be less than .002 inches. Ideally the tailstock end of the work-piece will be slightly higher than the headstock end.
Finally, insert a tool or test bar into the taper of the tailstock quill. Indicate along the length of the tool or test bar on both the top and side. These readings should match the readings you took on the quill. If they don’t, then the tailstock taper is not in line with the quill's outside diameter.
If the tailstock alignment errors exceed the tolerances shown, you should consider a realignment. This is a fairly common problem on lathes and grinders on which the tailstock is used extensively.
The ways of the tailstock wear more quickly because the lubrication system on most tailstocks is suspect, at best, and because dirt and grinding grit get under the tailstock when it's moved. The tailstock is subject to a lot of contamination because it's always unclamped when it's moved. If the guide ways haven’t been wiped off prior to moving the tailstock, then dirt creeps in. To make matters worse, some operators clamp the tailstock down on the dirt, embedding it in the slide and worsening the problem.
So, if you do a lot of work between centers, or need to drill and ream precision holes using your lathe, check out that tailstock alignment and have any realignment issues remedied.
Whatever you do, I recommend that you maintain a metal-to-metal fit between the tailstock and the bed of the machine. Do not allow anyone to “build up” the tailstock ways with a non-metallic way liner. These materials will not hold up to the dirt and repeated clamping cycles.
Having a premium lube system pays off by Jim Leigh, Pyramid Rebuild & Machine co-owner
If you're undertaking a major rebuild or repair to a machine tool, take time during the process to evaluate the machine's way lube system, which, if operating improperly, can cause major damage.
Many machine tools are supplied with a lubrication system that connects a series of meters or orifices in parallel with each other.
The weakness of this type of arrangement, known as a parallel system, is that if a meter plugs, that lube point gets no oil and there is no signal of the failure back to the operator. With a parallel system, virtually all your lube ports can be blocked and you won't know it. This will significantly wear the machine's ways and may necessitate having it realigned.
Some lube systems are better than others and it's wise to use the best available. If you're rebuilding or realigning a machine tool, I strongly recommend installing what's known as a "series progressive lubrication system" because of its ability to provide feedback to the operator. With a series progressive, you'll know if you have a blocked port.
The system uses divider valves to deliver a controlled volume of oil to each lube point. Because these divider valves are connected in series, each valve must cycle before the next one in the series. A high pressure switch signals the operator if a blocked lube port occurs.
Other feedback devices that are available with a series progressive include cycle completion switches and broken-line indicators.
Proper installation of a series progressive lube system is the key to maximizing its benefit. During installation one common problem to look for is one lube port feeding more than one way surface. This type of porting creates a parallel route for oil to travel and defeats the purpose of the series progressive. So, inspect all slides and plug parallel paths. Drill new oil ports so that each way surface has its own lube port.
I'm often told series progressive systems are too expensive. My experience doesn’t bear that out.
The way lube system protects the heart and soul of your machine tool. Compared to the expense of repairing ways damaged by poor lubrication, the cost of a series progressive lube system is minimal. We wouldn’t skimp on the lubrication components for our cars. Why would we do so on our machine tools?
Tips on grinder care by Jim Leigh, Pyramid Rebuild & Machine co-owner
1. Clean the machines. The swarf created by the grinding process is abrasive and works its way into a grinder's clearance areas and elsewhere. This problem — common on rotary and centerless grinders — can cause serious damage.
2. Regularly examine your coolant and adjust the mixture according to the manufacturer's instructions.
3. Many machines require repair because of lubrication system failures. Most way lube systems on grinders are terminal and require that lube levels be maintained.
4. Remove the gibs on the vertical slide and clean them at least once every six months. Coolant mist dries on the gibs, making them dirty and prone to sticking, which often causes excessive wear on the vertical leadscrew.
5. Check gib adjustments regularly and don't adjust them too tightly, which can cause excessive wear on the machine slides and drive train.
6. Remove the magnet from your surface grinder at least twice a year and stone the table top and magnet surface.
7. Remove the swivel table (sub-table) from your cylindrical grinder twice a year and treat it the same as the magnet mentioned in tip six.
8. On rotary grinders, check the stone segment clamps and clamp screws. Replace any that are bent, worn or damaged. Also inspect the tapped holes in the wheel and repair any stripped holes. Failing to maintain the wheel can result in “dropped” stones and serious damage.
9. On surface grinders, remove the grinding wheel and clean the wheel adaptor, spindle and all threaded pieces. Use an anti-seize compound on all components when putting them back on. Be sure to replace wheel blotters and balance the wheel.
10. Inspect and repair or replace any damaged way covers and water guards. Neglecting to maintain these components can damage way surfaces, which is likely to necessitate a machine realignment.
A simple way to check machine tool geometry by Jim Leigh, Pyramid Rebuild & Machine co-owner
Today’s CNC mills are popular because they produce high-quality workpieces faster than ever. And while we count on skilled machinists and sophisticated CNCs to compensate for backlash and positioning errors, we shouldn't expect them to make up for machine-tool geometry flaws too.
These problems cause errors in almost every aspect of the part. The more accurate your parts must be, the better your machine geometry has to be, so it's wise to evaluate it. Though there are several ways to do so, the following methods are quick, require only basic tools and produce reliable results. They also can be used on any machine tool with one horizontal axis or more.
If you've already confirmed spindle tram and axis squareness and are still having problems with your workpiece geometry, these level readings should reveal two of the most common geometry problems on milling machines: axis pitch and axis roll. Pitch refers to an axis rising or falling. Roll refers to an axis that's twisting.
Let's get started. You'll need a master level, a little patience and about half an hour.
When the master level is placed on the working surface of the machine table, you should be able to move the table anywhere along its travel path and maintain a consistent level reading. If you can’t, you’ll know you have a problem and further testing may be required.
Here’s a procedure for taking the reading referred to above:
1. Place the master precision level (.0005”/ft accuracy) on the table so that it's parallel to its length. Move the table to its extreme right-hand travel position. Adjust the level to “zero,” if necessary. Now move the table about 36” or to the center of travel, whichever is less. The level reading should still be within one line of your original reading. Record the reading and take additional readings as you move the table in 36” increments until you reach the left-hand travel limit. Compare each reading
For most applications, no two consecutive readings should vary by more than .0005”/ft. and the total leveling error should not exceed .001” for an axis with 72” or less of travel. High precision applications will require more accurate leveling.
If your readings exceed these measurements you may have a problem with axis alignment or machine leveling.
It's a good idea to repeat this step three times. Once with the level in the center of the table, once with the level at the extreme right and once with the level at the extreme left.
2. You're largely repeating the procedure outlined in step 1, except you rotate the level ninety degrees, reset to “zero” if necessary, and then take your readings, comparing them as before and applying the same accuracy standard. Remember to take three sets of readings: right, center and left.
3. Repeat step 1 again, only now you'll take readings while moving the saddle in and out. Check at 36” increments and compare your readings to the standard above.
4. Repeat step 3, but place the level at ninety degrees. Take your readings and compare them to the standard.
These same tests can be applied to a conventional lathe as follows:
• Place a master level (.0005”/ft accuracy) on the lathe saddle so that it's parallel to the bed's length. Move the saddle to its extreme right-hand travel position. Adjust the level to “zero” if necessary. Now move the saddle about 36” or to the center of travel, whichever is less. This level reading should still be within one line of your original level reading. Record the reading and move in 36” increments or until you reach the left-hand travel limit.
• Repeat the above procedure. But this time rotate the level ninety degrees, reset “zero” if you need to and take your readings. Again, compare your readings using the same standard as previously mentioned.
As you can see, similar tests using these principles can be developed for virtually any type of machine tool. Remember this machine-tool principal, though: It's usually unimportant if the machine is setting perfectly level “to the world,” but it is important that each axis be in a true plane.
Proper geometry is built into quality machine tools. With correct set-up, maintenance and care, that geometry should be sustained for several years. But as a machine tool wears, squareness, straightness, and parallelism are compromised, and suddenly you're fighting to produce parts that are accurate.
The simple steps described above will permit you to evaluate your machine geometry to determine if it's the culprit, and they will help you keep your machines on the level.
Tips on trouble-free machine tool installation by Jim Leigh, Pyramid Rebuild & Machine co-owner
1. Prepare a proper foundation; it's critical if you want top performance from a machine. Follow the manufacturer’s foundation requirements closely, or contact contractors that specialize in this type of work.
2. Consider all the utilities your machine will require and plan their availability early in the project.
3. Plan your machine's location wisely. Often overlooked when installing large machine tools is crane access for aid in maintenance and repairs.
4. Address repairs up-front when installing a used machine. Significant savings can be achieved if repairs are done as part of the installation.
5. Allow adequate floor space for storing a disassembled machine.
6. Provide appropriate anchoring and leveling hardware. For most large machine tools, cast-in-place anchors are best.
7. Schedule time for machine alignment, leveling and calibration. This is particularly important when installing large machine tools, which sometimes require several days to perform these vital procedures.
8. Remember to factor in a period to troubleshoot your newly installed machine. The time needed will vary depending on the complexity of the installation and the type of machine control.
9. Test-run the newly installed equipment so any bugs can be eliminated.
10. Replace or repair missing protective guarding and make sure guardrails are properly installed. Confirm that pits and tanks are guarded and post signs at confined spaces. Finally, ensure that the machine is correctly grounded and that all energy sources can be locked out.
The last word: Whenever you install a machine, everyone asks, "When can we turn it over to production?" Use these tips to develop an installation timeline that's aggressive, yet realistic.
When done right, machine tool retrofit can save thousands of dollars
by Jim Leigh, Pyramid Rebuild & Machine co-owner
When compared with the expense of buying new equipment, a machine tool retrofit can save thousands of dollars. But to get the most bang for the buck from the project, there are some key details you should consider to help the process be as successful and as economical as possible.
First of all, make a detailed assessment of the machine. Ask yourself, what is it capable of doing now, what are its shortcomings, and what would you like it to be able to do once the retrofit is completed.
Remember, this is an ideal opportunity to customize a machine tool to fit your exact needs.
Next, consider the options and issues that typically crop up during a machine tool retrofit and that must be addressed when developing the specifications for the job.
In cases where you're simply replacing a control on an existing piece of CNC equipment, the list of these options and issues is shorter.
For a machine that's being converted from manual to CNC, the list is longer, but taking time to consider each of these factors is worth it.
So, let’s take a look at some items you'll need to remember when writing your specifications.
• Feeds and speeds: Develop a specification for each axis and spindle involved. Be realistic. Rebuilders and integrators can make the machine tool do just about anything – for a price. If you really need 1200 IPM rapids, specify it. If not, save yourself the money.
• Feedback systems: Consider whether you want motor-mounted encoders, leadscrew-mounted encoders or linear encoders. Each system has its uses. Talk to your integrator to get the best match for your needs.
• Operator station or HMI: Choose from among the many options that exist, including screen size and type, touch-screens, pushbuttons, over-rides, electronic handwheels and remote stations. Also think about whether you want the operator station to be pendant-mounted or enclosed in a console. Consider height, range of motion and other ergonomic factors.
• Jog functions: Determine whether you need incremental jog? If so, what increments? Continuous jog? If so, what speeds? Think about whether you need to jog a spindle, CW or CCW.
• Ancillary equipment: Specify all the items that are to be controlled, including the coolant pump, chillers, and the hydraulic and lubrication systems. Regarding the latter two system types, you may have one or more of each to deal with.
• Machine layout issues: Give thought to the location of the machine and all related equipment such as enclosures, isolation transformers and motor-control centers.
Environmental conditions in the shop can have an impact on the project, as well. For instance, if you experience high ambient temperatures in your workplace, consider auxiliary cooling for electrical enclosures and servo motors that operate at low speed.
Also needing lay-out decisions are the machine's conduit runs. Should they be in a power trough? Will they be overhead, rigid, EMT or sealtight?
• Mechanical Issues: Another mechanical issue that's best addressed during a retrofit is alignment.
To achieve maximum accuracy and rigidity from your machine tool, the guideways and related components must fit properly. Looseness, because of wear or improper adjustment, may result in geometry errors in your part, as well as poor surface finishes and shortened tool life. New CNC controls can compensate for many shortcomings, but they can do nothing about rigidity loss and shortened tool life.
You can perform some simple alignment checks yourself. (See the article, "A simple way to check machine tool geometry.")
If you find problems or are dealing with a major retrofit, hire a specialist to check out machine alignment. Machine alignment is best left to those who deal with it daily. It's simple, but not easy. A professional will choose the right way-lining materials for your application and restore the ways to like-new condition.
Along with the ways themselves, examine the systems that lube the ways. Now is the time to install a new series-progressive way-lube system. (See the April 2006 Nuts & Bolts for more information on these.)
Maximize the benefits of these systems by using the CNC to control pre-lube cycles, and on and off times. Not only will the ways get properly lubricated, you'll save oil and energy by delivering the lube only when needed and in the proper amount.
I recommend installing new way covers on every retrofitted machine tool. Realignment of the machine ways is usually the single-most expensive element of a retrofit project. Protecting that investment with properly designed way covers just makes sense.
By following the steps recommended above, you should complete the project with a retrofitted machine that you're happy with and a bill that you can live with, as well.
How to prevent accuracy from slipping away by Jim Leigh, Pyramid Rebuild & Machine co-owner
1. Re-position the vise on the table of a manual mill to even out slide wear.
2. On surface grinders, move small work pieces to different locations on the magnet.
3. On any machine tool, manual or CNC, run the slides to their extreme travel limits daily to even out the wear.
4. Inspect lube levels daily. Make sure all machine-tool slide components are being lubricated.
5. Check way cover systems frequently and make necessary repairs.
6. Clean the ways. A simple wipe-down of exposed guide-ways significantly reduces slide wear.
7. Maintain coolant at proper pH level. Poorly maintained, spent coolant can cause severe damage to ways and other machine components.
8. Inspect and maintain the level on all machine tools. This is especially important on machine tools with long beds, like roll grinders, lathes and planer mills.
9. Don't use compressed air to clean machine tools. Vacuum the machines instead.
10. Don't overload the machine tool with work pieces that are beyond the designed capacity of the machine.
Gib adjustments reduce wear by Jim Leigh, Pyramid Rebuild & Machine co-owner
Proper maintenance of machine-tool slides is critical if you want to maximize machine-tool life. However, even the best-maintained machine tools will wear eventually, and the looseness in the slides that results will cause geometry, accuracy and tooling problems.
Routine adjustment of the gib will help reduce the wear's effect. On most machines, the gib is an adjustable, tapered slide component that is used to compensate for normal wear in the machine-tool way system.
Over the years, I've heard a lot of misinformation about adjusting these components. The fact is, there is nothing mysterious about it. There are several techniques to properly adjust the gibs. Here's the one I use.
Start by removing the way covers, and if necessary, clean the ways and apply a light coating of oil. Then, run the slide throughout the length of its travel. If it's a manual machine, note the effort required to move the slide at the ends versus in the center. If it's a motorized machine (CNC or otherwise), use an ammeter to monitor the amperage required to move the slide along its length.
On a machine with even wear of the slide components – including lead screws, guide ways, gibs and straps – the effort (amperage) along the length of the travel will be consistent. If the effort required varies, chances are your machine tool is wearing unevenly.
Let’s assume effort is consistent. In that case, use this method to adjust the gib:
Run the slide to its extreme right or left position. Use an indicator to determine the actual looseness in the slide at this position. Adjust the gib slowly and monitor your progress with the indicator. Keep adjusting until the slide looseness is less than .0004.”
For most mills, lathes and machining centers this will be tight enough. Remember that looseness and deflection are two different things.
There will always be deflection. No matter how tight you adjust a gib, you will always see some movement or deflection. If you are deflecting the slide, the indicator will move away from the “zero” under load then return to zero when the load is released. This deflection is often several thousandths of an inch. If the slide is actually loose, the indicator will deflect under load but will not return to zero when the load is released.
Reduce this looseness to .0004" or less by adjusting the gib. Now, move the slide throughout the length of its travel and monitor the effort required.
If normal effort is required without any tight areas, you're finished. If tight areas are detected, note their position along the axis and readjust the gib when the slide is at this position. On a well-maintained machine tool, the effort will be consistent, crisp and smooth.
Go slowly if your application calls for tighter gib adjustments. Remember that a gib that is overly tight will produce jerky, stiff movement and premature wear on drive components.
Rigging safety is a must by Jim Leigh, Pyramid Rebuild & Machine co-owner
Though too often ignored, rigging safety is literally a matter of life and death. Fail to observe the rules and principles of proper rigging when moving heavy loads and someone could die or get badly hurt. At best, a rigging mishap will hurt your wallet, forcing you to deal with damaged equipment. Either way, it's just not worth it. Take the time to learn about rigging safely and strictly follow the correct guidelines. Here are some of the primary ones.
Know the working load limits of your rigging equipment, such as cranes, chains, slings, eyebolts and anchor shackles. This critical information can typically be found on the equipment itself. If you can't locate it, contact the equipment manufacturer or its sales representative. Whatever you do, don't guess. The reason for knowing the working load limits of your rigging equipment is obvious – you must not exceed them.
Lifting angles are another vital consideration regarding rigging safety because they can compromise working load limits. For example, chains are strongest when they're placed under a load at an angle of 90 degrees to the horizon. If you rig chains at an angle, you shrink their working load limit.
How many times have you heard the expression "the right tool for the right job"? That maxim certainly applies to rigging. When you plan a rigging project, use the proper equipment for the task. For instance, lifting eyebolts are ideal in situations in which a load is applied parallel to the eyebolt's axis. But if you use the same eyebolt for a side-load lift, which applies force at an angle to the eyebolt, that's an inappropriate and potentially perilous application. Swivel hoist rings work best for side-load purposes.
How do you know if you're using the proper component? Study rigging principles, get training and ask questions.
There's no question about the need to protect the machine tool component being lifted or conversely, the rigging equipment being used. Padding serves as the buffer between the piece and the rigging component, be it a chain or a sling. Padding material can be improvised from discarded rubber belting, chunks of old fire hose or worn-out nylon slings that have been chopped into pieces.
Without padding, a chain under load can chew into precision surfaces. If you're using a nylon sling to hoist a machine tool component, padding is necessary to shield the sling from the piece's hard angles, which can be transformed into knife-like blades under load.
Finally, institute rigorous inspection standards regarding your rigging components. Check them periodically and just before each lift to ensure they meet the manufacturer's standards.
Does it take time to do this? Sure, just as it takes time to learn and practice the principles of safe rigging. But it's time well spent when weighed against the potential tragedy and expense of a rigging accident.
Ten tips to make your machine tools last by Jim Leigh, Pyramid Rebuild & Machine co-owner
Ever know someone who slapped down thousands in cash for a good car and then ruined it by failing to properly maintain it? The same thing occurs with machine tools, though the value of the investment is typically much higher than that of a new auto. That's why it's smart to adhere to these common-sense practices to squeeze more life out of your equipment:
1. Follow the OEM maintenance inspection schedule — obvious advice that's often ignored.
2. Don't neutralize features aimed at protecting the machine, such as pressure and limit switches, and low-fluid level indicators.
3. Maintain way lube levels.
4. Be wary of way lube levels that don't change. It could be a sign of a faulty lube system.
5. Monitor a machine's coolant levels and preserve the proper coolant mixture.
6. Remember that cleanliness is king when it comes to machine tools. Brush 'em down. Wipe 'em off.
7. Do your level-best to keep a machine tool level. Out-of-kilter machines suffer irregular and accelerated wear.
8. Maintain cooling units such as chillers to ensure ideal spindle-bearing temperatures.
9. Replace or repair damaged way covers, which shield precision way surfaces.
10. Keep the doors on electrical boxes closed. Leaving them open allows contaminants to invade these sensitive spaces.
Finding run-out cause takes detective work by Jim Leigh, Pyramid Rebuild & Machine co-owner
One of the fundamental aspects of machine tool accuracy is establishing a precise fit between the machine's spindle and the tool that fits into it. If this critical pairing is less than perfect, you'll likely experience run-out. And if that occurs, you'll probably encounter one or all of these problems:
• Failure to achieve work-piece repeatability.
• Inability to attain hole roundness.
• Excessive tool wear.
When run-out troubles like these arise, it's easy to blame the spindle taper and call in a specialist to perform a spindle taper regrinding. Regrinding the taper will certainly restore the precision fit, but its effectiveness is limited if there are other faults lurking in the machine tool spindle. Should underlying problems exist, you can have the spindle taper reground as much as you want and your run-out issues will continue.
Before shelling out good money for taper regrinding, take the time to do some detective work, which involves making a few simple checks to discover exactly what malfunction you’re dealing with.
First, use a dial indicator to measure the run-out on the outside diameter of the spindle. To do that, take one reading while turning the spindle clockwise and take another while rotating it counter-clockwise. If the spindle on the machine tool extends and retracts, take the clockwise and counter-clockwise readings with the spindle in both the extended and retracted positions.
Your readings should be within a couple of 10ths (.0001) of one another. If they're not, your spindle bearings may be loose or worn. With extend-and-retract type spindles, too large of a difference in the readings suggests a poor fit between the spindle and its housing.
Still another task you should perform before diagnosing spindle taper as the source of your run-out troubles is to inspect for axial slip.
To do that, take two measurements, with the first at the present spindle position. Next, rotate the spindle 180 degrees and take the second measurement. The slip should be between .0004 and .0008. Anything beyond those parameters is unacceptable.
As you can probably guess by now, if you have a spindle with a bearing or fit problem, or if its axial slip is out of whack, taper regrinding will have little benefit until you remedy the problems in the spindle itself.
PYRAMID Rebuild & Machine LLC
Rebuild It, Reuse It ... Make It Last
123 S. Thomas Road Tallmadge, Ohio 44278