Way lapping, Scraping, Gib adjustment and Lock screws


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Thread: Way lapping, Scraping, Gib adjustment and Lock screws

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    Default Way lapping, Scraping, Gib adjustment and Lock screws

    Hello All,

    I too have an IH mill. Got it the first part of March, lapped the ways and am using it manually until I have the coin to acquire Aaron's CNC kit. The mill is a real chunk-of-a-machine, and I like it alot.

    Two points here. Lapping the ways went fine, though it is work--my bursitic shoulders complained for a week. Well, I was fortunate to attend the CNC Workshop at Cardinal Engineering where they retrofitted one of the Grizzly round-column mills. One thing I took real notice of was the out-of-the-box quality of the ways: nice looking hand scraping and smooth travel (I don't know how to guage it other than by looks and quality of travel) all with NO LAPPING. This made an impression on me.

    Now, my travel is fine, but it is fine because I lapped the ways. And it's not as pretty as the scraped ways, but that's no big deal.

    My second point: The gibs in the Grizzly unit were adjusted to their working position with the locking screws REMOVED. Well, the gibs in my mill REQUIRE the lock screws to be adjusted to engage the gib in order to be in the working position. If the lock screws are not engaged, the table can be slightly swiveled or rocked in the the X-Y plane with the gib adjustment screws fully screwed to the extent of the adjustment range.

    The significance of this did not become apparent to me until after I returned from the workshop and was thinking about what I had observed. That is, that the locking screws are being used for a purpose not intended, and the wear is going to be concentrated on two points rather than over the full range of the gibs.

    What do you folks think about this???

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    David,

    I think you lapped your ways a lot or you also lapped the dovetails or a combination of both. I had this same problem with my Y axis. The gibb strip is tapered, and notched. Inserting some shim stock behind the nonmovement side of the gibb strip will actually improve the fit better than original as the shimstock will be more uniform than the surface. Cut a notch in the gibb strip shim to match the gibb strip as in the picture below and see if you can get the gibb strip to go in enough to eliminate the play. My shim is 0.005" thick.

    Here's a trick to make it easier - use a carbide point scribe to scribe an outline of the gibb strip on the shimstock including the notch in the strip and you can flex the stock to breakout the shim from the stock.

    These aren't $15,000 machines and a little shim stock here and there doesn't hurt anything.

    I also was disappointed with the condition of the ways on my machine and a few other blemishes on the table. I hope current machines are improved in this regard. Having said that, I am willing to work around those issues for the advantages of the large table, long column, inch lead screws and the hardened gearset. Another advantage is Aaron, he's honest, and willing to tell you the good and bad of things with no bull.

    Let us know how things work out David.

    Welcome to the world of the "Big Mill".

    Mike

    Attached Thumbnails Attached Thumbnails Way lapping, Scraping, Gib adjustment and Lock screws-gibstrip-shim_1_1-jpg  
    Last edited by MikeAber; 08-05-2005 at 02:40 AM.


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    Bursitis sucks. I race motocross and have separated each shoulder more times than I can count - each time I have a shoulder injury, bursitis kicks in.

    Sleep with a heating pad wrapped around your shoulder for three or four nights - it's the only think I have found that eliminates it and it works very well.

    ...and that's about all I have to contribute to this thread....

    Scott

    Consistency is a good thing....unless you're consistently an idiot.


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    MIke,

    That's a good idea, and precisely how I'll move forward. I concur on all counts about the mill and Aaron.

    Scott,

    Heat is what I use on my shoulders as well... I've walked with a cain for years, and using your arms for legs puts stress on the wrists and shoulders they were never designed for.

    Regards to all!!



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    Hi Mike and Dave,

    Thanks for enlightening me on the gib adjustment. I have the same issue so far on the Z slide. Gib is all the way in. I would need to use the locking screws to tighten the gibs further.
    I haven't assembled the X and Y far enough yet to know if I will have the same problem on those gibs as well.
    Thanks for the tip Mike.

    Regards,
    Chris



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    Exclamation Take it Easy

    It seems that we have been taught since birth that if a little is good, then more is better. Lapping your ways is one of those exceptions, Less is better!

    To everyone without experience lapping the ways:
    Just take the tops off of the rough (high) spots, you do not want 100% contact. I recommend you skip the coarse grades of grit entirely and start with 320 (#77) grit. Do not worry about how the ways look - just that they are smooth in operation. The low spots hold the oil to keep the ways lubricated.

    The type of media you use also has a profound effect on how fast and how long the surfaces are smoothed. Silicon Carbide does not break down into smaller pieces as you continue the smoothing process. Clover Compounds are formulated from silicon carbide and other special-purpose abrasives. Silicon Carbide compounds will make the process go faster, not necessarily better. Any Silicon Carbide abrasive left behind will continue to cut until it is removed. Aluminum Oxide compounds left behind will continue to break down slowly into smaller pieces until they no longer cut anything. Timesaver media is my favorite lapping media as it does not embed itself into the metal as Silicon Carbide and Aluminum Oxide do.

    "Timesaver Lapping Compound does not contain emery, aluminum oxide, silicon-carbide or similar charging abrasives. They are unconditionally guaranteed not to imbed into any metal surface. Prepared in powder form, to be mixed with oil as used. Timesaver first acts as an abrasive, then the particles diminish to a polish, and finally to inert material. TIMESAVER can be used on any hard metal friction surfaces where accurate fits are required, such as valve seats, machine tool ways, tool room applications, etc."

    This is the right stuff to lap ways with: http://www.newmantools.com/lapping/time.htm#green
    TIMESAVER GREEN LABEL GRADES FOR HARD METALS
    (Steel, Cast Iron, Hard Bronze and Stainless Steel)
    #55 Coarse #77 Medium #111 Fine #333 Very Fine

    I would not lap the dovetails unless they are noticeably rough. If you find the dovetails to be rough - a few strokes with 600 or 800 (#111) grit with the gibb strips in place should make them noticeably smoother and a gentle stoning of the gibb strips is fine. While you are at this stage with everything apart take a moment to remove those razor sharp edges with a fine mill file or india oil stone - don't get carried away with large radiuses, just break the sharp edge so it can't cut you or someone else.

    This should clear up some of the confusion and common mistakes made lapping ways.

    If you decide to lap your ways, you are responsible for the results. No one at CNC Zone including myself, the site owner and site provider are responsible for the results.


    Mike

    Attached Thumbnails Attached Thumbnails Way lapping, Scraping, Gib adjustment and Lock screws-timgreen-gif  
    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Quote Originally Posted by MikeAber
    Do not worry about how the ways look - just that they are smooth in operation. The low spots hold the oil to keep the ways lubricated.
    That's why I'm scraping instead of lapping them. The small pockets you get when scraping are acts as oil reservoirs.



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    Hi Einar,

    If you have the skills to scrape the ways your method is superior to lapping and the prefered method.

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Sharp edges

    ... While you are at this stage with everything apart take a moment to remove those razor sharp edges with a fine mill file or india oil stone - don't get carried away with large radiuses, just break the sharp edge so it can't cut you or someone else.

    This should clear up some of the confusion and common mistakes made lapping ways.

    If you decide to lap your ways, you are responsible for the results. No one at CNC Zone including myself, the site owner and site provider are responsible for the results.

    Mike

    Mike, thanks for the input. While I followed Aaron's instructions quite closely, it is certainly possible that I over-did the lapping, though I truly doubt that I removed enough material to cause the current condition. Rather I suspect the Asian folks responsible for that particular function missed the target. But who knows for sure?? Not me.

    I would add one further comment on the "sharp corners" point. It is important to leave the sharp corners on the ends of the sliding way edge untouched. Reason being is to have that sharp corner plough all chips from the way surface. A less-than-sharp corner can allow small chips to be "ridden over" and cause binding and/or wear.



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    Hi Don,

    I exercised great caution lapping the ways on my machine and I am sure you did as well. The fact that so many have lapped the ways indicates that there is room for improvement in this area. I would have gladly paid an extra $100.00 to have an acceptable set of ways in the crate when I opened it. My $1,000.00 Harbor Freight gearhead mill didn't have this problem.

    You are right, it is important to leave the sharp corners on the ends of the sliding way edge untouched.

    Mike

    Last edited by MikeAber; 07-21-2005 at 06:00 PM.
    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Twenty five years ago when I was throughly involved in machine tool rebuilds scrapping was considered the only valid way to fit a machine together. Though I see mention of lapping ways all over the internet, it is not something I care to suggest. The reality is the more you do it the more the surface deviates from an ideal plane.

    The only time a stone gets near a set of ways being reworked is right after a scrapping session. That is only to remove burrs or high spots.

    So I'm with ES take the time to scrap the surfaces in correctly if needed.

    Thanks
    dave



    Quote Originally Posted by ESjaavik
    That's why I'm scraping instead of lapping them. The small pockets you get when scraping are acts as oil reservoirs.




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    Wizzard,

    Unfortunately, some of these Chinese mills don't have an Ideal plane on them (like mine) and most of us (hobbyists) don't have the skills to correct the situation with the prefered method (scrapeing). If I had the money for a Bridgeport or other fine machine in the same class I would agree with you 1000%.
    It's difficult for some to rationalize the difference between a $15,000 commercial machine and a $1,700 Hobby Machine. The hobby machine is as huge a compromise in quality, fit and finish as lapping the ways is a compromise to scrapeing the ways.

    You and ESjaavik are both right. Would you come and fix my ways for me the correct way? Please!

    Mike

    Last edited by MikeAber; 07-21-2005 at 06:03 PM.
    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    I have an Enco version of this mill. I am converting the mill to CNC via IH goodies. I lapped the ways slightly, mostly just to clean it up slightly.

    As for the tapered gib strips. I had the problem of not being able to tighten them down enough to take up excess movement. After examining the adjusting screw with the gib out I determined the screw was too long. It was bottoming in the threaded hole before bottoming at the head. I shortened the screw enough to be able to bottom out the head and still able to grab the slot on the gib while installing it. I did this on Z and X axis and can now lock the travel up if I wanted too.

    On a side note. The two locking screws are not for applying gib friction or tension. They are to be used as axis locking screws as on a Bridgeport. For example: while milling along the X axis only lock the Y axis.

    JRouche

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Gib Strip Shims

    I cut another notch in my gib strip so it would go in further.

    I discussed this subject with Aaron this week and his method is to push the gib strip all the way in without the screw until you lock up the axis, then mark the strip with a pencil or sharpie then pull the strip back out to the place where the screw engages the threads three or four turns and make another mark on the gib strip. Pull the gib strip out and measure the thickness with a mic at the two marks - the difference between the two is the thickness of the shim you need. By using a shim you will have a full range of adjustment to compensate for wear in the future. So far, I like the gib strip shim method best.

    Mike

    Last edited by MikeAber; 07-29-2005 at 03:40 AM.


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    Please please please don't let lapping compound near any way/dovetail/etc or any other bearing surface - doing so makes as much sense as pouring the compound into you crankcase - there's little difference; you are voluntarily putting grit into a bearing that will wear metal away in an uncontrolled manner. Sorry if that’s harsh, but it would a real shame someone reading this thinking that lapping the ways was ok to do.

    MikeAber seemed carefull to point out it was used sparingly and with fine grit, but regardless, as others have mentioned, lapping is not a substitute for scraping. if there is something wrong with the ways, you've got to identify exactly what is wrong and correct that. something not straight, not parallel, not flat etc. This is done by scraping as scraping is very localized - material is removed from exactly where you want to remove it from to solve the problem whereas lapping is wholesale material removal from everywhere. Scraping is not hard to learn (hard on the arms though).

    lapping two parts together will not produce either flat, aligned or parallel parts. In a machine, all it will do is produce slop. If its a poor finish or burrs you are concerned about, break off a 3 inch piece of a worn, very fine file and skim over the surface with this. If the ways just aren’t as true as you’d like, you can ether live with it, hire it out or learn to scrape – lapping will only add to the problem. It may seem like it moves more smoothly, but only because you’ve increased the clearance (slop) between the mating surfaces; you have not made said surfaces flatter, straighter, etc. Ideally what you want is a very small clearance because the surfaces are perfectly flat and parallel, you fine tune or restore that alignment by scraping

    If you have tried to lap, first thing you need to do is get all the compound out if it’s not already. this means complete disassembly and several washes/scrubs with kerosene. If you have possibly gone too far, to tell if you’ve damage it, you need a reference flat. Unfortunately they aren’t cheap but you could make one by scraping a piece of cast iron using a surface plate. any metal will do, but cast iron is less likely to move over time. using a surface plate. and you'll need it anyway if you're going to scrape

    Last edited by Mcgyver; 08-03-2005 at 08:51 AM.


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    Quote Originally Posted by MikeAber
    Wizzard,

    Unfortunately, some of these Chinese mills don't have an Ideal plane on them (like mine) and most of us (hobbyists) don't have the skills to correct the situation with the prefered method (scrapeing). If I had the money for a Bridgeport or other fine machine in the same class I would agree with you 1000%.
    My issue is that you run a very real risk of making your machine worst, much worst in fact. It really doesn't matter if the mill is a Bridgeport or a chinese mill the problem is the same. Also even though it is described as a hobbiest machine thses small mills have a great potential when operated within their desgin limits. The key here is to keep the machine in good shape or even improve it a bit.
    It's difficult for some to rationalize the difference between a $15,000 commercial machine and a $1,700 Hobby Machine. The hobby machine is as huge a compromise in quality, fit and finish as lapping the ways is a compromise to scrapeing the ways.
    I disagree here, anybody that has been around machine tools can see the differrences between a hobby machine and a commercial machine. Do realize though that the machines in this forum often straddle the line between the two uses.

    The hobby machine is certainly limited in many respects but the reality is that lapping ways is not an improvement at all. The point is if you want it to work better, it has the potential. That requires a bit of fine tuning, the only way to achive that at the hobbiest price point is to scrape the ways.

    You and ESjaavik are both right. Would you come and fix my ways for me the correct way? Please!

    Mike
    Mike you can do the job yourself with an old file and a flat surface and a beveled straight edge. Surface plates are pretty cheap now a days and is likely to be something that you will appreciate in the future. There are a couple books that describe how.

    Thanks
    Dave



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    Talking Way Lapping & Scraping, My Final Comments

    This is an endless debate and you guys are still right!

    To have this job done by a professional could cost more than the machine. I own several scrapers, a surface plate, Prussian blue, and a book on the subject and I'm still not comfortable with my skills. If I had a skilled craftsman here to confirm my skills and provide guidance I probably would have gone the other way.

    There's a big difference between reading something in a book and doing it correctly, or even understanding why it is or is not correct. It may be that you have years and years of experience and training to guide your hands. I have no experience or training to guide my hand. I'm a computer and electronics guy, I could tell you that installing DNS or DHCP Servers for 4,000 clients is easy and Active Directory is a piece of cake. There are books on those subjects. You may not be that confident without classroom or personalized training.

    I have no experience at how to determine if the ways are true, twisted, offset, upset, mad or lying. I do know they were very rough in comparison to the ways on my other mill and lathe. I swept the table with a DTI and determined that the before and after readings are within a couple of tenths and the table is just as lousy after the job as it was before the lap job. The table runs flat within +/- .0005" in 20" on the X axis with a .005" rise on the left side in the last 5" and a .007" rise on the right side in the last 5" of travel due to the weight of the table hanging out there. The Y axis is +/- .0005" in 10" with .001 from the front to the back of the table, the same as before. Movement is smooth and predictable, my gibbs are run tight, the power feed isn't complaining any more and I'm not complaining either.

    I agree with your position; however I also feel there is room for another solution if done in moderation. If I could do this all over again, I would do so, just a little less than before. If I had the skills and confidence in those skills, I would scrape the ways. Will I lap the ways on my other mill or lathe? Absolutely not! They aren't broken. Am I going to continue to discuss this issue? - I don't think so - foolish; or not, it's already been done.

    I appreciate your comments and advice. I believe everyone has learned from this discussion. You are still right; scraping is the preferred method if you have the skills, I don't.

    Last edited by MikeAber; 08-04-2005 at 05:46 AM.


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    Where did you find the book and tools to scrape ways?

    I have seen people do it, and have an older lathe I would like to see how much damage (well hopefully improve it) I can do.

    Anybody got any good tips, websites, videos, ?? on scrapping ways? It seems like a quickly dieing art.



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    For everything you ever wanted to know about machine tool reconditioning, this is the tome
    http://www.powells.com/cgi-bin/bibli...4-1114266612-0

    One day I’ll buy, haven’t bothered yet.

    Scrapping is a bit of a funny thing in that the way many react to it it’s like a black art or that several generations of English metal workers were of uncommonly high intelligence (well that may be). The reality is you could compare it to tapping; kind of neat and no big deal once you’ve done it. Just like tapping there are fancy things you can acquire and sometimes its challenge (like 1mm into stainless), but like tapping, for the average application its not beyond anyone’s ability – heck I’m a week warrior and have successful used scraping many times.

    Here are the basics. You need a flat reference (surface plate will do), a work piece (piece of AL or cast iron if you have it) a scraper (made from old file, see fig 2254 2252 attached) and Prussian blue (old paint that doesn’t dry, available form msc etc).

    Get a section of your work somewhat flat by filing/milling, whatever. Smear a thin coat of blue onto the reference. Rub the work on the reference. Pick it up and look where you rubbed it - notice the blue marks in the piece. Place the work in a vice and use the scraper, held sort of like a large wood chisel using two hands (see attachment), repeat repeat and repeat until the entire surface picks up the blue, or until your wrist falls off. You can get fancy, for example certain wrist movements can produce the gull wing shape, but it doesn’t do anything and sprung the boredom and tedium of someone scraping for months on end.

    You now know how to scrape. It’s a valuable shop technique and is not just for machine tool reconditioning. Tooling can be scraped (i.e. angle plates, etc) to perfection and you can develop a surface on a casting or part so that clamping to a table for other operations won’t distort it (even a surface grinders magnetic chuck will distort things) etc. You can scrape round shapes as well so now all your plain bearings will be smooth as silk.

    Btw the attachment was taken from Modern Machine Shop Practice, New York: C. Scribner's Sons, 1887-88. you can DL it at http://digital.lib.msu.edu/collectio...m?AuthorID=138
    Beautiful illustrations, and although 120 years old, a lot of good content.

    I’ll try to take some pictures of some scrapers tonight and post them if there is interest. Sorry to be verbose, just want to encourage those interested to give it a try, its not that hard and is a valuable technique in the shop

    Attached Thumbnails Attached Thumbnails Way lapping, Scraping, Gib adjustment and Lock screws-pages-asbch25-pdf  


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    Thumbs up Yes!

    Finally; Someone willing to help the situation.

    Thanks for taking the time to get envolved Mcgyver!

    Please continue to give us guidance and enlightenment.

    My Book: http://www.lindsaybks.com/bks9/hscrape/

    Last edited by MikeAber; 08-04-2005 at 01:53 PM.


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