Way lapping, Scraping, Gib adjustment and Lock screws

[haysys]

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???

[MikeAber]

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

[mxtras]

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

[haysys]

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!!

[ChrisJ]

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

[MikeAber]

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

[ESjaavik]

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.

[MikeAber]

Hi Einar,

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

[haysys]

... 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.

[MikeAber]

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

[wizard]

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

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.

[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%.
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