Lathe taking a deeper cut then dialed in on the DRO.

[Just for fun]

I had a little time this evening to look at the lathe. I found that there was 4 thou of movement in compound slide. I tightened it up to the point it's too tight when I crank it all the way in and 1.5 thou in the middle of the throw.

So, yesterday I didn't lock down compound, that would have helped. Tonight after I adjusted the compound gib and locked it down repeated the cut from yesterday kind of. I zeroed out like in Stefan's video and then took another 5 thousand off. This time when it got to the bigger end, it took 1/2 thousand off more then the rest of the cut. I don't know if that is acceptable or not but seems pretty good at this point.

I need to look at the gib adjustment again as it's not right. On the small end the gib the adjustment screw wants to walk over top of the end of it. If I get the gib just a little tight I can't loosen it with the other screw. It's hard to explain but I have to loosen the screw next to the hand wheel all the way out and then move the gib with a screw driver, then try and tighten it up again but not too tight. I'll call Precision Mathews tomorrow.

 

[compact8]

.... I have to loosen the screw next to the hand wheel all the way out and then move the gib with a screw driver, then try and tighten it up again but not too tight. I'll call Precision Mathews tomorrow.

Is it a tapered gib ?

 

[Jake P]

I need to look at the gib adjustment again as it's not right. On the small end the gib the adjustment screw wants to walk over top of the end of it. If I get the gib just a little tight I can't loosen it with the other screw. It's hard to explain but I have to loosen the screw next to the hand wheel all the way out and then move the gib with a screw driver, then try and tighten it up again but not too tight. I'll call Precision Mathews tomorrow.

What you are describing sounds similar to what I found with my 1440gt.

I’m not sure if the screw riding over the gib was due to the previous owner not understanding how the gib adjustment worked and he just overtightened it or the gib end was not machined correctly. The end of the gib ended up being rounded off allowing the screw head to ride up on it.

I simply reground the end of the gib. There’s plenty of length in the gib (at least on mine) to shorten it a bit and still be fully functional.

 

[Just for fun]

Thanks Jake, Grinding the end would do no good. It's like it is too short width wise, the screw head just barley hits the gib.


Here are a couple photos. And now I see they don't really show it like I was hoping.

 

[Jake P]

Thanks Jake, Grinding the end would do no good. It's like it is too short width wise, the screw head just barley hits the gib.


Here are a couple photos. And now I see they don't really show it like I was hoping.

View attachment 406611

View attachment 406612

Yes, there’s just not enough there! Mine looked the same in there was that part where the screw head had ridden over the edge (I should say the gib has gone under the screw head), but the gouged area was far deeper.

I think the problem with mine is the same as yours but to a much lesser degree. When I figured out why I couldn’t get a consistent gib setting for my compound and got it solved it was my assessment that the geometry of this setup was wrong. But I luckily had enough material to work with, you apparently don’t.

You did buy your machine new, correct? PM should make it good. I bought my machine from the original buyer and PM does not have a path for warranty transfer unfortunately.

 

[compact8]

For your reference the gib of the compound slide on my bench lathe ( Emco Compact 8 ) has got divots for accomodating the end of the screw + pin assembly so the adjustment screws are always pressing against the center of the gib.

 

[Just for fun]

For your reference the gib of the compound slide on my bench lathe ( Emco Compact 8 ) has got divots for accomodating the end of the screw + pin assembly so the adjustment screws are always pressing against the center of the gib.

View attachment 406707

That looks like a good setup. On the PM-1236T the gib is tapered with a screw at each end for adjustment. And only one screw to lock the compound like yours. It seems to me that two locking screws would work better. I guess a solid tool post would even be better.

 

[Just for fun]

I talked to Mike at Precision Mathews today and he recommended that I make some sort of washer to push on the gib. He said a replacement wasn't as easy as just sending a new one as they are hand fitted.

So here is what ai came up with, it works pretty well. I had to shorten the small end of the gib to get the adjustment I wanted. All in all, I'm really not all that happy with the compound and the adjustment. It's either too tight or loss where it feels good moving it in and out but at that point, I have 2 to 3 thousands movement from side to side at the end of the end of the compound. When I lock it down I can still move it at least 1 thousand. It seems to me that two locking screws would be better, and I may do that just to see what happens. I can see where a solid tool post would solve the problem.

Anyway, here is the spacer/washer that I made for the gib adjustment.

 

[compact8]

It appears to me that the sloppiness is due to the taper angle of the gib being inaccurate. It must be machined or replaced if a good replacement can be found. I will use a solid tool post as a temporary solution.

 

[erikmannie]

I wonder how much a new compound would cost.