SL-20 Tailstock backs itself off

[DruMor]

Last night while checking a part's OD measurement, I noticed the tailstock backed off +/-.050ish from being tight against the part. I thought it was a fluke, but it has done it again this morning. On the position screen when the TS is loose, B has moved itself +.1 (reads in .1's) positive somehow. Sight glass on hydraulic tank shows it is full. My tailstock hold point is .200 inside the part, pressure set to 300PSI. I have made this same part with the same program and same setup for several years. I thought if the tailstock moved in cycle that the machine would alarm out.

I'm at my wits end with this. This part has 2 tight tolerance OD areas that get turned and this problem has already messed one part up. Where do I need to be looking for a problem?

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[djr76]

Could be the comb looking thing and the sensor behind the ts way cover is all dirty and needs a good cleaning. Happened to me recently, iso alcohol solved it.

[DruMor]

I appreciate the reply. It wouldn't surprise me that stuff behind the TS way cover could be the problem. This machine cuts a lot of cast iron and that stuff GETS IN EVERYWHERE!

After my original post, I left the machine on for a few hours while doing other work and according the the position screen, the TS moved back .7" over the course of a few hours. We will get the way covers yanked off this thing and see what we find.

Thanks!

[HAASTECHMAN]

So you say the tailstock creeps back on its own?? If this is the case you may have a hydraulic valve issue. Possibly the reverse valve is getting pressure from the forward side. Chips in the covers can cause the tail stock to stop short but it won't creep back. Some machines have the "comb" others don't. Some have a servo tail stock. Most are hydraulic. Some don't have B home switches and the control assumes when the comb stops reading the hash marks, it's home sometimes when it's not. This causes overshoot of tail stock.

[DruMor]

So you say the tailstock creeps back on its own?? If this is the case you may have a hydraulic valve issue. Possibly the reverse valve is getting pressure from the forward side. Chips in the covers can cause the tail stock to stop short but it won't creep back. Some machines have the "comb" others don't. Some have a servo tail stock. Most are hydraulic. Some don't have B home switches and the control assumes when the comb stops reading the hash marks, it's home sometimes when it's not. This causes overshoot of tail stock.

I guess our next step then is to look at the hydraulic valve. We got it put back together other than the way covers yesterday and it still creeped back. Some of the fingers on the comb were bent, and we can't figure out how that happened.

The machine is a 2001 model if that tells you anything.

Thanks for the information

[HAASTECHMAN]

Chips get in everywhere and ruin all sorts of stuff. I am constantly amazed at where I find them. You can straighten the comb, as long as it does hit going through the reader. 2001 is pretty generic year. look into the valve assy.