# Making a gib for my lathe-



## ErichKeane (Sep 5, 2019)

SO, Full backstory: https://www.hobby-machinist.com/threads/how-do-i-make-this-gib-materials-order-of-operations.79423/

For those who don't want to read, my 14" Reed Prentice lathe's compound slide gib was pretty messed up, so I opted to make a new one!  I am following some of the advice in that thread.  

First, I ordered a piece of Class 40 Cast Iron from Speedy Metals.  

Next, I cleaned my table and retrammed the head (I used this https://www.edgetechnologyproducts.com/pro-tram-system-01-000-10-000-09-000/).  I'd prevoiusly had the whole machine apart, so the head was quite a bit out of tram, despite aligning it with a square.  



While that was happening, I also cut my 24" piece of stock in half.  I ordered 1.25" square stock, 24" long.  I need ~10-11 inches (and much less than 1.25"!), but ordered 2x as much so that I have 2-4 chances in case I mess up.



The stock was actually REALLY flat from speedy metals, surprisingly so!  On the table, I couldn't get .003 shim stock under it anywhere!  I flattened 1 side to be a reference surface anyway, but I had to swap 3 clamps around.  I ended up taking ~.008 off, but the 2nd pass was likely unnecessary.



I flipped it over and did it again   This will be the new 'top' of my gib.  



Next, I indicated along the back side to minimize the amount of material I needed to take off.  I'd initially done this with a combo square off the front of the table and was only off ~3 thou over the whole length!  A little bit of tapping, and it was just about perfect.



Next, I cut enough material off the back to remove the rounded top.  Initially, I'd planned on this being the dovetail side, but it isn't going to work out that way, so cutting this much material off ended up being unnecessary.  



Next, I was going to cut the dovetail, however ran into a huge problem: I have a riser block, so even with the spindle all the way extended, the table all the way up,  and quite a bit of stickout, I'm still about 3/8" too high!  




SO, I'm going to cut the "flat"/"overhang" side on the back.  I can use the same endmill as before and just take the 0.130 off the back instead.  I am just going to use 1-2-3 blocks under the stock when I flip it around to do the dovetail side.

I came up with ANOTHER significant issue however that I wouldn't mind feedback on.  The nose of the dovetail (the acute side) is rounded over a bit, so measurements off of it aren't terribly accurate.  Any amount that I miss this 'radius' is going to significantly alter the size.  At the moment, my solution is going to be to just make it 'close' but a bit oversized.  Then, I plan on just doing a set of test/fit cycles.  I don't have a good, repeatable way to put it back on the mill (since I'll have removed most of the material from the 'bottom' as it sits on the mill now), so my ideas are:

1- If I end up too large, put some ~600 grit sandpaper on my surface plate, and take a few swipes at a time off the dovetail.  

2- If I end up being too 'small', take some brass shim-stock and loctite it to the flat (which is not a moving surface).

Thoughts?


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## RJSakowski (Sep 5, 2019)

What type of gib are you making?  I have seen two types of gib design, one where the gib is adjusted by a series of set screws and a second where the gib is tapered  and adjusted by moving the gib lengthwise in a similarly tapered space.  

The first type really only has one critical surface, the side that contacts the moving dovetail.  It isn't even necessary that the gib have parallel sides as the back side is held away from contact by the adjustment screws.  

The second type is considerably more critical as for any section along its length, the two contact faces have to be parallel and the taper has to exactly match the taper of the ways.  Given that the taper is usually not specified, this becomes a trial and error exercise.  If the original gib was not in too bad a shape, it could be used as a backing plate to set the taper angle, at least to rough the new gib in but scraping would be needed to properly seat the new gib.

The two non contact faces are not critical.  I would mill them using an angle vise or sine plate rather than using a dovetail cutter.


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## ErichKeane (Sep 5, 2019)

RJSakowski said:


> What type of gib are you making?  I have seen two types of gib design, one where the gib is adjusted by a series of set screws and a second where the gib is tapered  and adjusted by moving the gib lengthwise in a similarly tapered space.


Its the second, it is a tapered gib adjusted by a screw that pushes it lengthwise.



RJSakowski said:


> The first type really only has one critical surface, the side that contacts the moving dovetail.  It isn't even necessary that the gib have parallel sides as the back side is held away from contact by the adjustment screws.
> 
> The second type is considerably more critical as for any section along its length, the two contact faces have to be parallel and the taper has to exactly match the taper of the ways.  Given that the taper is usually not specified, this becomes a trial and error exercise.  If the original gib was not in too bad a shape, it could be used as a backing plate to set the taper angle, at least to rough the new gib in but scraping would be needed to properly seat the new gib.



I have at least a good 6" of the original gib that I intend to use as the backing plate to set the taper angle.  I don't know anything about scraping, so I was hoping I could "scrape" it in with sandpaper.



RJSakowski said:


> The two non contact faces are not critical.  I would mill them using an angle vise or sine plate rather than using a dovetail cutter.


I have neither of those.  I have a sin bar, but I couldn't come up with a way to use it to mount this.  The dovetail cutter is cutting a contact surface, so I'm hoping it ends up being close enough to work.


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## machPete99 (Sep 5, 2019)

I have not done this, but you should probably check out this video on the subject by Stefan Gotteswinter:


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## ErichKeane (Sep 5, 2019)

machPete99 said:


> I have not done this, but you should probably check out this video on the subject by Stefan Gotteswinter:


I'd watched that a few weeks ago. Is there something in particular you think I've messed up? I only have a 1 direction taper, which makes a lot of what he does unnecessary.


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## machPete99 (Sep 5, 2019)

I think all of these gibs are only tapered in one dimension, and I thought that was what he was doing.
The geometry is still a bit tricky to get your head wrapped around, but I figured that he is a pretty good machinist so is probably doing it the right way.
You typically end up with a parallelogram shape in looking at the end, and getting those angles layed out correctly can be tricky.
Like I said, I don't have the answers here, but may go through this on one of my machines one day, so if you figure out a simpler way please document it!
--mP


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## machPete99 (Sep 5, 2019)

On you measurement issue, I would try to use a dowel pin or small length pf drill rod, diameter of which should be a bit under the total height (.542) probably around 0.500 diamter. Put the dowel pin against the angle surface, that way you are measuring somewhere in the middle, and reference from the bottom surface. Do this on the original and new part in similar locations to compare. That way you are not measuring at the sharp (or not so sharp) edge. You could probably also achiece this using a similar size ball bearing for a single contact point, which might even be better.

I would also be tempted to arrange for the part to be held at the correct angle and use a straight end mill to machine, similar to Gotteswinter. That also gets the part up into your work envelope.

If your table is level you might be able to use a sine bar and machinist level to read the original angle, as well as setting the work holder to cut the new one. You would need a square bar with a vee notch along its length cut with a straight end mill, with head tilted at a 30* angle. This bar would then be tilted in the vise to get the proper taper.


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## ErichKeane (Sep 5, 2019)

machPete99 said:


> On you measurement issue, I would try to use a dowel pin or small length pf drill rod, diameter of which should be a bit under the total height (.542) probably around 0.500 diamter. Put the dowel pin against the angle surface, that way you are measuring somewhere in the middle, and reference from the bottom surface. Do this on the original and new part in similar locations to compare. That way you are not measuring at the sharp (or not so sharp) edge. You could probably also achiece this using a similar size ball bearing for a single contact point, which might even be better.


I just don't have a good surface to reference the dowel pin off of though.  Typically you do that on the inside of something, but I don't really have that.  I'm at a bit of a loss.


machPete99 said:


> I would also be tempted to arrange for the part to be held at the correct angle and use a straight end mill to machine, similar to Gotteswinter. That also gets the part up into your work envelope.
> 
> If your table is level you might be able to use a sine bar and machinist level to read the original angle, as well as setting the work holder to cut the new one. You would need a square bar with a vee notch along its length cut with a straight end mill, with head tilted at a 30* angle. This bar would then be tilted in the vise to get the proper taper.



My table isn't particularly level unfortunately, Its close, but not enough to measure off of.  My floor is wavy enough that it makes it pretty tough.  My head only spins left/right, not titlt up/down, so I'd have to do it on the Y axis, where I don't have that travel unfortunately.

Also unfortunately, the way I had to line it up (and the only way I had a machined surface) was to do it like below.  I used 1-2-3 blocks under my material and clamped it down.  Then I used 2 woodworking clamps (1 removed in the photo) to hold the old gib against the side on top of a parallel (so it would clear).  I used a straightedge to keep them as even as possible al the way across.

I got it dialed in about 5 tenths over about 10 inches, which is about all the good material in the old gib.  I didn't make cut, but I plan on re-indicating tomorrow and trying a cut.


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## Cadillac (Sep 5, 2019)

Using your old gib to reference the angle is what you want that's how you do it.


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## ErichKeane (Sep 6, 2019)

Cadillac said:


> Using your old gib to reference the angle is what you want that's how you do it.


Yep! That's what is on the top of that stack!


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## machPete99 (Sep 6, 2019)

If you can't come up with a way to measure the thickness you should plan to make the new gib extra long and cut off any extra after fitting it to the target machine. This is usually a good practice with these things from what I have seen.


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## ErichKeane (Sep 6, 2019)

machPete99 said:


> If you can't come up with a way to measure the thickness you should plan to make the new gib extra long and cut off any extra after fitting it to the target machine. This is usually a good practice with these things from what I have seen.


Yeah, I agree. I'm sadly right about  at the max envelope of my machine. Plus I already cut my material at a little more than 2 iinches oversized


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## ErichKeane (Sep 7, 2019)

Made a bunch of progress today!  I was able to cut the dovetail and get the piece cut off, and get it test fitted.

I clamped a parallel on the flat side near the camera, then put the old gib against it, and indicated against it. I got it to ~5 tenths along about 7 inches.  Then, I cut the taper with it clamped to the table with a roughing mill.




I cut until the small side was slightly larger than the small end of the gib I was copying.  You can see the shape, the little 'shelf' on the bottom right (1st step) is part of the piece, the rest is clearance on both sides.



I lined up the dovetail cutter to cut about the height I wanted.  A bit more stickout than I wanted, but I did only about 30 thou per pass.






Here's the dovetail basically done.  I think I did a spring pass right after this one to get it a bit smoother.




Someone had suggested a mag chuck, so thats what I did!  Onto the surface grinder it went!  I ended up having to take a bunch of material because my bandsaw cut wasn't anything close to even.







And here it is after!



I did a little bit of deburring, reassembled the lathe, and popped it in.  I tapped it in with my hand and moved the compound, and it seemed to work!  I'm a touch oversized, so the last inch or so isn't supported, but I intend to fix that on the surface plate with some fine grit sandpaper.  The compound moved smoothly and was tight, so I figure it is a success so far!


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## ErichKeane (Sep 14, 2019)

I forgot to take pictures of the rest of the process, but it was also quite educational.  When I first put it in, it went in, but stopped about 1.25" from full depth.  I blued the side, and ran the compound a few times and discovered that I was actually getting contact along just about the whole way.  My taper must have been pretty close!

So, I started sanding on my surface plate.  I was afraid at first of taking off too much material, so I started sanding with 1500 grit paper.  I spend about 2 hours going back and forth, and got no apparent progress.  I blued around the whole thing to make sure I wasn't binding anywhere else, and found I was still stopping on the taper.

SO, I switched to 300 grit paper.  I went back and forth for another 3 hours, and got to about 1.15 inches short (yes, I made 10 thou of progress in 3 hours...).  After calculating that that I was going to need the rest of my natural life to complete this, I tried 60 grit paper.  I made SOME progress, but the paper didn't last very long, so I went through my whole pack very quickly.

SO, I switched to files, where I found that about 30 minutes of filing would get me about 1/4" of progress!  A few more hours of filing, and it fit perfect!  I also found that with it at the full 'correct' depth, I could leave it at full length and it wouldn't interfere with anything!  I now have an extra 2" of material for the future! I cut the 200 thou slot in the side in the for the adjustment screw, and it was project complete!


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