Scraping a tapered gib

I figured we needed to start a new thread and get input from everyone, plus it can be archived better.

If it is a quality made machine and not a cheap Asian brand we can't talk about on here. Those builders use angle grinders to scrape and if you have one good luck. If you have one made by a craftsman then the builder knew what he was doing and did it right 99% of the time. If some so called mechanic worked on a quality machine and screwed it up to be like a poorly made Asian machine, you will have to use your mechanical ability to be a detective and do it right. Some Asian machines are top quality. I am speaking of the ones bought at a cheap website or cheap catalog. You know what I mean. Japan, Korea and Taiwan make some amazing machines used in industry.

Here is what I teach and use. This is exactly the way my Dad was taught and taught me. For those of you who don't know. I am a Journeyman Machine Tool Rebuilder and still rebuild machinery for a profession and teach it. You can look in my profile and see several pictures of scraping and rebuilding.

If the gib is in good shape I use the one you have. If the customer is not rich I reuse the old gib as it is the simplest repair or way to rebuild the gib. I know some like to make a new gib to keep it original, but in 999 out of a 1000 machines I have rebuilt I reuse the old gib. This is the method I use.

This after it was cleaned and checked for severe damage and the gib is still usable. You have made a gib holder that clamps the gib into a pocket like a vise and lays flat, slight pressure holds it in place, you use a magnetic chuck with demagnetizer. I do not recommend clamping on one side of the top of the gib and then the other on a table. A waste of time.

A student at Mars in Kansas showed this old dog a sweet and easy way to clamp a gib..a camm clamp He laid the gib on a mill table and in one T-Slot he put one clamp and in another T-Slot he put another so the gib was angled across the table. he used Untitled Document <> over the years I have made gib holders devises but this is a sweet and simple method. (I have a picture someplace of it, but their website shows the little cam clamps pretty good)

Before scraping the gib I have scraped the pocket it fits in. 75 % of the time the gib side of a way is high in the middle or the ends are buggered up.
You have the mating surface scraped parallel and to the number of points required. I say 20 PPI is easy if you follow my teaching as shown in other threads.

One VERY important thing to do is is to assure the back side of the gib mating surface is parallel to the opposite side of the way. I check this when I am match fitting the 2 parts when scraping them. On dovetail ways it is hard to keep the angles the same as it is easier to scrape the surface nearest to you and it is a pain to scrape at the bottom of the dovetail. That is why we use a hack saw or you grind the corner of a scraper blade thin to get down deep in the bottom so you do not leave a ledge down there. CONNELLY (book) shows a 3 bladed saw to remove the ledge, but I have never had much luck using one. I have used a single hack saw blade on smaller compounds, thin cut off wheel on a air grinder, knife file, stone, etc.

I hope this is not to confusing, but I will rub the way that the back side of the gib sets against the opposite side, or where the gib rides against. Before sliding in the gib cock the slide and rub that non riding side against the riding side to make those surfaces a mating fit. If not those angles may not be the same. You may have to file the sharp edge on each side back a bit so they don't hit. But this is a important step because if this is not parallel top too bottom of those surfaces the gib could cock especially when the gib is only held on one end.

The gib will drop on the un-supported end and tighten up making it look like the taper is off. Be sure that surface is flat and hinges (airy points) at 25 to 30% from each end. It is hard to check the hindge be sure to lift your straight edge out of the bottom of dovetail to get a good pivot or hinge. If you let the straight edge rest at the bottom of the dovetail it will always pivot on the ends, so be sure to pull it up a bit.

Then we do the Gib:

1. Stone and file off any burr's
2. Check and see if is straight on a surface plate. Measure how much with a feeler gage or indicator.
3. Straighten gib as close as you can get it, can't slide in a .0015" feeler on the unworn back side.
4. Scrape the back side of gib to get a -- Static Fit -- which is 2 to 5 PPI / 50 to 90 POP
5. Run a tap into the gib screw holes and check the fit of the screw in the pocket it goes in, if the gib has a notch, check it. Repair where needed.
6. Blue up the riding surfaces, even the ways you have scraped as it helps lube them so you don't gal them up while rubbing.
7. Slide in the gib, it will no doubt slide in to far so cut a plastic shim and fit it against the back side it can be loose. Put in the gib screw (s) and blue up the gib.

8. Check the taper now by leaving the gib loose approximately .002 on the tight end. If you leave it tight you will get a false reading. With the gib loose mount a mag base on the solid side close to the end of the way and put a .0005" indicator on the opposite side close to the end then push and pull the top slide and check for LOST MOTION or slop. it will be at least .002" Then move the mag base and indicator to the opposite end of gib and do the same. Push Pull to find the LOST MOTION and it will be at least .002" . If it is not the same then you will have to STEP SCRAPE the gib so the taper is the same on both end.

Scrape the gib to 20 PPI, same taper to .0002", relieve the middle 40% of blue spots .0005 to .001" low.

9. Now there are several ways to shim the gib permanently: I use one of the following methods on rebuilds: Turcite the front side of the gib, glue on Phenolic on back side or front side. I use grade LINEN and not the paper type. Then scrape the material to get a good fit and PPI. In a fast repair in an emergency I will glue a plastic shim to the back or use brass or steel shim stock fitted behind the gib.
10. Drill oil holes and cut oil groves.

More later.... time to make make breakfast. Hopefully some of you will add some info and photo's. Time for my students to TEACH. Rich

If anyone needs to make a tapered gib the sort you comes across in lathe cross slides and top slides and the like, when I was rebuilding the 10EE I wrote up a description of a jig I made up to make the process easier starting here

http://www.practicalmachinist.com/vb/monarch-lathes/ozee-rebuild-264941/index10.html#post2215258

This all very cool! I watched a video from one of your classes done in Sweden I think, very good stuff seeing what is becoming a lost art taught to folks all over the world.

So I'm trying to get an understanding of the concept of the tapered gib. (I do automatic transmission rebuilding for a living ) so which piece is tapered? I disassembled cleaned and painted, and reassembled our old Bridgeport, so i have some experience here. Some, lol. For example the table or saddle? Thanks for your time. Oh if you books or dvds I'm interested! Or come to Atlanta!

Just a trivia that I learned from John Knox, who worked as engineer for Sheldon till they closed and is very active in the Sheldon Yahoo forum: They machined their tapered gibs using shapers and the gibs so produced required minimal finishing. A few times somebody would came up with a plan to phase out the shapers and produce the gibs in a more efficient way. They tried several different processes, but they always went back to the shapers due to both a too high reject rate and too much finishing work required.
Essentially, the long, continuous stroke of shapers and planers introduces much less stress in these skinny pieces than milling.

Paolo

Rich,
I have scraped the ways and slides of a dovetail system and I am now scraping in the gib as a final step. The gib is 0.012" too small, so I need to make it grow. The only size phenolic LE I can find is 1/32" thick. I have a 0.010" plastic shim behind it right now. I would like to go to 0.012" since the gib is still sticking through a bit and I would like to use a material that I can glue on effectively and also scrape. Do you glue on the phenolic and then machine it down before you scrape? Is there a source of smaller sheets?
Jeff

Sorry I missed your question. I am on holiday. I buy Grade linen from this company and they sell .010" thickness. Phenolic Sheet | Phenolic Rod | Plastic Laminate You could glue it on with a super thin 5 min epoxy on the back side, but it will probably get destroyed after a while if there is a lock that screws into it. be sure to cut the oil slot prior to gluing as if you do it later the thin material will rip. I generally don't like doing this, but that's what you want. I generally grind the gib on a sign plate and glue .030" Rulon 142 to it. You can also cut some .010" steel or brass shim-stock and put it behind the gib, sometime in a fee state, depends on the situation. I also scrape the gib taper with the shim "before" final gluing on so no need to scrape it after it is glued. Be sure the gib is straight too.
Rich

When I repaired the gib on my 10EE. I used a piece out of a set of cheap chinese made feeler gauges and glued it onto the back of the gib.

did you then scrape it? probably not. how flat was it?

I was thinking of a couple of other fixes I have done over the years. At Midwestern Machinery where they used rebuild several machines and they had a crew of about 6 full time rebuilders, one full time machinist, 1 electrician and 1 welder fabricator. They would braze an extension cast on gibs to lenthen them and then mill or grind before scraping. If we were in a hurry and the gib was only a few thousands off and went to far and the gib screw bottomed out but the head of the gib screw stil had a 1/2 " under it before it bottomed out in the counter bore (typical design found in Bridgeport mill) I would cut off a 1/4" off the thread end of the bolt and use a bottom tap in the hole so I could get the small amount needed. I wouldthen cut off the small end of the gib so you could install the rear wiper cover. Not the best ways but it worked and never heard from the customer in this business "no news is good news" Rich

I am working on the tapered gib for the table on my mill.

It is about 22" long and 1.5" wide.
As near as I can tell I need about .013 of shim in order to get the screws back into a usable area.
Since I have some brass shim the right size but would have to buy the phenolic (or turcite), what is the downside to using metal?
If it is not a good idea I can always buy something (not in a hurry), but if I can use what I have that would be great.

Thanks!

I like it, Richard. Good post outlining a step by step approach to a topic some seem intent on mystifying.. The method you describe is simple, helpful and descriptive.

I suggest aspiring machine tool re-builders print this out and post it near your scraping station.

jkopel said:

I am working on the tapered gib for the table on my mill.
View attachment 167406
It is about 22" long and 1.5" wide.
As near as I can tell I need about .013 of shim in order to get the screws back into a usable area.
Since I have some brass shim the right size but would have to buy the phenolic (or turcite), what is the downside to using metal?
If it is not a good idea I can always buy something (not in a hurry), but if I can use what I have that would be great.

Thanks!

Click to expand...

Sure use the brass, but be sure to scrape and check the taper on both ends wih the shim in place. There are better ways to do it, but heck all machinists shim gibs his way and the machines last for another day. Rich

Richard King said:

Sorry I missed your question. I am on holiday. I buy Grade linen from this company and they sell .010" thickness. Phenolic Sheet | Phenolic Rod | Plastic Laminate You could glue it on with a super thin 5 min epoxy on the back side, but it will probably get destroyed after a while if there is a lock that screws into it. be sure to cut the oil slot prior to gluing as if you do it later the thin material will rip. I generally don't like doing this, but that's what you want. I generally grind the gib on a sign plate and glue .030" Rulon 142 to it. You can also cut some .010" steel or brass shim-stock and put it behind the gib, sometime in a fee state, depends on the situation. I also scrape the gib taper with the shim "before" final gluing on so no need to scrape it after it is glued. Be sure the gib is straight too.
Rich

Click to expand...

So I thought I had my practical machinist account set up to email me if someone replied to a thread I as on, so I'm just checking back now and realizing there are replies. Sorry, I would have been back earlier.

So Rich, I gather that I can do a lot of things to make the machine work, but the system that you find is the most solid and provides the most longevity, is one that uses a bonded piece of rulon or turcite. But since I've already gone down the road of scraping this machine in without rulon or turcite, would it make sense to put rulon on just the gib? Would that pose any unevenness issues? Presumably it's not too late for me to glue on a piece of rulon to the other side as well, but I've just got all that work done already.

Unless you're suggesting gluing rulon onto the back of the gib, but then it seems you don't get the value of the expensive antifriction material and one might as well use a metal shim. Correct? Would the locks ruin the turcite as well?

Bottom line is I'd like to do it correctly, so I'm brainstorming on how to pivot my plans. You suggest grinding the gib on the surface grinder. My surface grinder is large enough for two of the three gibs, but I do not have a sine plate that would work to hold such a long slender part. Do you have any tricks other than just buying or building a sine plate? I guess I might be able to come up with a rudimentary one pretty easily, but it won't be magnetized. I guess I could outsource the grinding as well.

When I am out on a job and they don't have a magnetic or plane sign plate, I loosen the chuck and slide in a long pin or shaft under the low end and roll it in to raise that end and then tighten down the chuck snug, not reefed.

You are over thinking the turcite on the gib problem. It is not that complicated to bond the Rulon or Turcite to the wear side. I would never put soft Turcite on the back of a gib ...did you read this

" I buy Grade linen from this company and they sell .010" thickness. Phenolic Sheet | Phenolic Rod | Plastic Laminate You could glue it on with a super thin 5 min epoxy on the back side, but it will probably get destroyed after a while if there is a lock that screws into it."

If I warned you above that the hard Phenolic might get squished don't you think I would say the Turcite would get squished because it is a softer material?
Also thinking of the difference of how the friction of cast on cast vs. Turcite on one side and none on the other side is not an issue. This is not rocket science. Rich

Maybe I'm wrong and over-thinking it a bit myself. But I think the point Jeff is making is that (if I understand correctly) that gib is also used to to lock the element (I don't recall if it is the saddle, the knee, the table, or whatever) in place, by pushing it against the mating dovetail. If this is indeed the case, wouldn't the lower friction of those materials interfere with the locking action (like it's a no-no putting Turcite under the base of the tailstock of a lathe)?

Paolo

Not to be a crab or insult anyone here.
Well sure the Rulon on the wear side will slip, but this is all speculation. What I read when Jeff asked the question is he is worried that the side with the Rulon will be slipperier then the cast iron side and that would cause more creep on one side or the other.

(Added 4/30) I have seen a real problem with the lock not holding when you retrofit a Bridgeport type knee mill when you use Rulon/turcite and install a ball screw. That is why many of the newer machines have double locks on the table. But if your staying with the Acme feed screw you should be fine.

I have never had a customer complain about the lock not holding when I have used Rulon/Turcite on a gib. On a Bridgeport the lock is a bit of a joke anyway. On a new machine or a good used machine with the lock snug you can move the table. Hell many times when a machine is loose I have seen machinists leave the lock tight to get it to cut better when climb milling.
You Brainiacs go ahead and calculate the PSI and the shore hardness scale vs the Coefficient of friction. That's above my pay grade. Maybe you can write professor Slocum or Midland and all those MIT grads in the Boston class to work with you to figure it out. :-)

Go ahead and have at it. From Tri-star:

Other key characteristics of the aqua-colored Rulon 142 are virtual elimination of stick/slip, uniform friction, high thermal dissipation, and good stability. And like all variations of Rulon, Rulon 142 delivers long wear, self-lubrication, and design diversity.

Rulon 142│ For Linear Bearings and Slides - TriStar Plastics Corp . Rich

I agree, once turcite is introduced, friction based locks are null and void IMO, a leadscrew pinch lock forward the leadscrew nut is what I make for machines I rebuild running all turcite slides. It is time consuming to add but it's solid and it works very well.
When the user tells me they don't use the lock I will just rebuild the factory setup letting them know that the lock will only make it "tougher" to move. No amount of friction can stop a material who's coefficient of friction increases with PSI applied.

Richard King said:

When I am out on a job and they don't have a magnetic or plane sign plate, I loosen the chuck and slide in a long pin or shaft under the low end and roll it in to raise that end and then tighten down the chuck snug, not reefed.

You are over thinking the turcite on the gib problem. It is not that complicated to bond the Rulon or Turcite to the wear side. I would never put soft Turcite on the back of a gib ...did you read this

" I buy Grade linen from this company and they sell .010" thickness. Phenolic Sheet | Phenolic Rod | Plastic Laminate You could glue it on with a super thin 5 min epoxy on the back side, but it will probably get destroyed after a while if there is a lock that screws into it."

If I warned you above that the hard Phenolic might get squished don't you think I would say the Turcite would get squished because it is a softer material?
Also thinking of the difference of how the friction of cast on cast vs. Turcite on one side and none on the other side is not an issue. This is not rocket science. Rich

Click to expand...

New to this. I have a tendency to over think things. Thanks for the mag chuck suggestion.