PM935 T-slot Width Variances

[kb58]

This is more a public service notice than an outright complaint, though it does make one wonder.

I bought 5/8" Kurt vise keys for their 6" DX6, thinking that it would be an accurate and easy (though not cheap) solution to keying the vise to the center T-slot—hah.

The PM935 manual does recommend vise keys, but notes, "...The T-slots on PM TS and TV mills are nominally 5/8", but check before working on the keys." Good advice, because the two outer T-slots measure 0.626", but the center slot, the one I wanted to use, measures 0.618". Did they use a different cutter on only the center slot(?), or were they just sloppy? Obviously, it's not hard* to mill down the keys to fit, but one has to wonder what that did at the factory.

If I had followed the manual and measured the center slot first, I wouldn't have bought these keys. Oh, and I did consider mounting the vice to one of the outer slots, but it ends up too cantilevered for comfort, and probably affects accuracy.

* Well, it might be hard, literally, since the keys are probably heat treated.

 

[Bob Korves]

Store bought t-nuts are hardened and often not nicely finished. The sizing of t-nuts is nominal at best, but so are many t-slots. I make my own t-nuts from mild steel to the fit I prefer, and round all edges and corners carefully. t-slots are a precision part of the machine, and should be cared for just as well as the ways and table surface. The hard t-nuts can be hard on the t-slots, they cause wear and galling. In my opinion...

 

[markba633csi]

I suppose the factory cuts the initial slot in more than one pass, before using the t-slot cutter. Probably normal variation for import machines
Possibly you could recut the slot using the machine itself but I would hesitate to do that
Mark

 

[wrmiller]

Store bought t-nuts are hardened and often not nicely finished. The sizing of t-nuts is nominal at best, but so are many t-slots. I make my own t-nuts from mild steel to the fit I prefer, and round all edges and corners carefully. t-slots are a precision part of the machine, and should be cared for just as well as the ways and table surface. The hard t-nuts can be hard on the t-slots, they cause wear and galling. In my opinion...

+1

 

[RJSakowski]

I would expect that the center slot was cut undersized for precision grinding to final size and perhaps the slot wasn't ground?

 

[kb58]

I wondered that myself, but will cut or grind down the keys instead!

 

[Clock work]

In case this is useful, like "note B" under the table: https://www.webpal.org/SAFE/aaarecovery/5_simple_technology/Machinery's Hndbk/26663_yj8.pdf

When positioning my Kurt on the table with kurt keys, there was no immediate engagement. There was a coating that prevented it which I had to remove. I can't recall now but I think I removed it with a razor and then stoned it. Even after that, my three slots are different sizes.

 

[kb58]

Good point. I did use WD40 on the center T-slot, hoping that it would open it up... nope. Before doing anything else though, I'll use a stone and run it down the sides to remove whatever else is in there. Since it's about 0.006" undersize, that's only 0.003" per side, so "maybe" it's paint or a rough coating. Fingers crossed.

 

[kb58]

To finish this thread, I spent about five minutes on each T-nut, rubbing them over a stone just enough so they'd drop into the slot. Problem solved.