7x12 ML tailstock slipping

[Nates]

Hi folks, first post:

I have a Cummins 7x12, and ever since the cam lock mod ages ago the tailstock slips badly enough that I pretty much can't use it for drilling. I think it's a cam travel range issue. I shimmed with a washer but since the plate only fits one way, the shim does nothing if it's equal to one thread pitch. I'm wondering about the best fix - if maybe the best bet might be to cut the M10 bolt off and drill the plate and use a separate nut, or if it's some other issue I should look into.

 

[homebrewed]

Is the cam lock layout such that the forces would tend to loosen it, i.e., cause it to rotate the wrong way? If so perhaps you can shim the setup to move the cam to its self-tightening position.

It also may be that the cam eccentricity is too great so its mechanical advantage is insufficient to firmly lock the tailstock down.

I'm using a different approach. I replaced the original 10mm nut with a threaded piece that accepts a tommy bar, basically drilled 4 holes in it. If clearance between the carriage and tailstock is a problem I use an allen wrench to tighten it -- the right angle portion of the wrench makes it easier to get in there and tighten the nut down.

Marking the nut to identify the most convenient points for the holes would have been really smart but I didn't think that far ahead.....

 

[Nates]

The cam is completely hidden behind a C-clip but I brought it in the house for further inspection after the kid goes go bed tonight

 

[homebrewed]

The cam is completely hidden behind a C-clip but I brought it in the house for further inspection after the kid goes go bed tonight

Your reply suggests that you purchased the cam lock mechanism (I made an unwarranted assumption that you had made it yourself). If so maybe it has a manufacturing flaw; or perhaps it actually is for a different model of lathe.

 

[Nates]

I purchased parts to convert it, but that was like 20 years ago, and I don't recall much about the parts/source/process.

 

[Nates]

It actually feels pretty snug, just won't hold up to drilling. But I just backed it up with a carriage stop and that cured it. I'll get around to fixing it right after the current project, and maybe see about wiring a carriage stop with a switch to kill the motor so I can power feed to the stop

 

[Firstram]

I had the same problem.
If the clamping plate has a stud, it limits your adjustment to 360° increments. This winds up either too loose or too tight at the optimal cam position. Change it to flat plate with a hole and a bolt you'll be able to adjust the length to work perfectly with the cam throw!

 

[Nates]

That was pretty much the solution I was planning. Just need to buy a stud and grind that one off and drill it.