Problem With PM1340GT Compound Base Lock.

[bretthl]

I went to cut an external thread, set the compound at 29.5 degrees and one of the bolts would not tighten. Removed the compound without rotating and low and behold the lock nut is positioned exactly at the insertion point. Any ideas how to fix this? This just happened, I have cut many threads with the compound at this position. It is to the point where I can no longer lock the compound base anywhere near 29.5 +/- 2 degrees.

 

[dpb]

Remove your cross slide, make a new t-nut entry hole through the bottom, and a larger t-nut.

 

[JimDawson]

Remove your cross slide, make a new t-nut entry hold through the bottom, and a larger t-nut.

Yup, that's what I would do also.

Here are some T-nuts I made for a project. The same shape would work for your compound. I made these on my CNC mill, but they could have been made on a manual mill with a rotary table.

 

[dpb]

They can be the same general shape as your existing t-nuts, just larger. Your t-nuts are sized for the existing entry hole, and to go around the corner between the entry channel, and the circular channel. If you make a larger hole in the underside of the circular channel, you can use a much larger t-nut.

 

[mksj]

Never seemed to have a problem with mine. It looks like the nut needs to be turned 90 degrees from it current orientation, but if just spinning in that position may have damaged the slot, then I would make a longer nut as others outlined. Alternative which I ended up doing was just using the cross slide to cut the thread and not the compound.

 

[bretthl]

Never seemed to have a problem with mine. It looks like the nut needs to be turned 90 degrees from it current orientation, but if just spinning in that position may have damaged the slot, then I would make a longer nut as others outlined. Alternative which I ended up doing was just using the cross slide to cut the thread and not the compound.

The slot is not damaged. It is just a poorly designed location for an entry hole. The most common orientation for a compound and they pick that for an entry hole. It agravates me that I have to waste time messing with BS like this.

 

[jbolt]

It is just a poorly designed location for an entry hole.

Yup, same for the PM1440-GT. One of my few pet peeves of the lathe. The T-nuts are also under designed and lend to excessive flex under heavy loads. One of the reasons I went to a solid tool post riser and only put the compound on for doing short tapers. The cross slide needs to be redesigned to have the entry hole on the bottom with a more substantial T-nut.

 

[rogerl]

Could you put the T Nut back in the slot and then make a plug to go into the entry hole? It would do nothing for making the T-Nuts stronger but it would keep them from falling out. It would save taking the cross slide off.

Just a thought

Roger L

 

[Cadillac]

My lathe is of same design but also has a through hole on the bottom. Always wondered why there is the hole on top if one on the bottom on mine?
I had seen acouple people end up cracking off pieces of the flange because the t bolt wasn’t supporting the underside correctly. If you look at your t-nut they are cut wrong to follow the t-slot in the carriage. The outside should be convex and the inside should be concave so it fits the slot snug. Your t-nuts are only supporting nubs in the slot.
When I went through my carriage that was one thing I did. T-nuts are as large as I could get in there and milled to follow the slot like explained. Fortunate for me my hole is at the 3:00 position and much smaller than in your pic.
The plug idea in the above post is a good one too.

 

[bretthl]

As flimsy as this cross slide is I really hesitate to mill a slot although that would allow installation of a much larger T-nut and concave/convex as Cadi and JD mentioned. I will try making the nut as large as possible and contour to go around the corner. Another time wasting PM upgrade (I hate this lathe).