# Qctp Question



## wrmiller (Mar 18, 2015)

I have a Dorian BXA that I am putting on a 13" swing lathe and it has two pins that go into the t-nut. This I assume is to keep the tool post from twisting under load on heavier cuts, but is it really necessary on a 13" lathe? Reason I ask is that I cannot set to 29.5 (or any other angle for that matter) while it's pinned and I really don't want to have to remove the tool post (to remove the pins) to set an angle. Opinions welcome.


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## roadie33 (Mar 18, 2015)

From Dorian info:
"An anti-rotation system is built into the tool post with anti-rotation pins, which are engaged with a "T" Nut or compound to provide maximum rigidity and stability when performing drilling, boring and heavy roughing operations."

It does talk about just using the center bolt for mounting so they might be removable.


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## wrmiller (Mar 18, 2015)

Hey Mike,

They are removable. They are just hardened pins in a bag right now. 

So I guess if I was going to do some heavy turning or boring I could put them in just for the safety factor. But most of my work is fairly light stuff so I think I'll default to leaving them out unless I need them. Thanks.


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## f350ca (Mar 18, 2015)

I have a Dorian CXA on a heavy 16 inch lathe. Don't recall pins coming with it, but maybe they did. Anyway it never moves under the heaviest cuts with no pins.

Greg


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## Andre (Mar 18, 2015)

If you ever drill using the carriage, I'd drill two holes (using a mill with a DRO, and a little Trig) in the bottom of the toolpost, so that when the compound it set at 29.5  the pins align the toolpost square to the lathe Z axis. On regular cuts I think it will be fine (the undersized AXA on my 13" never slipped) but when drilling who knows, it might help.


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## coolidge (Mar 18, 2015)

They use those QCTP on some CNC lathes Bill which can apply quite a lot of force, hence the video I posted recently of a QCTP twisting during a heavy cut and ripping the chuck off the lathe sending it flying at the operator's head. This whole 30 degree stuff I'm beginning to scoff at that. Sure if the ways and screws are sloppy. CNC lathes go straight at it and have no problem turning nice threads. I may just pin my QCTP and set it square.


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## darkzero (Mar 18, 2015)

I've mentioned this feature a few times around here.....

The only time I have ever needed to use the pins was doing a full form knurl on 1.25" ti 6-4 in one pass. Other than that, never needed them for anything else. I can max out DOC for my lathe's limit before the tool post will spin.


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## wrmiller (Mar 18, 2015)

Interesting you say that Charles, as the last few times I've done single point threading I did exactly the same thing. The threading came out good enough to register a titanium compensator whose septum's only have .006" larger bore than the bullet diameter. Guess maybe I shouldn't worry about it any more. Thanks!


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## wrmiller (Mar 18, 2015)

darkzero said:


> I've mentioned this feature a few times around here.....
> 
> The only time I have ever needed to use the pins was doing a full form knurl on 1.25" ti 6-4 in one pass. Other than that, never needed them for anything else. I can max out DOC for my lathe's limit before the tool post will spin.



Good points Will, this is only a 2HP lathe. I'm not even sure I will ever approach the max DOC on this thing doing what I do. I'm probably WAY over thinking this. 

Oh, and Will: Your pic reminded me of those little allen set screws on the side of the tool post. What are those for, adjusting the sliding piece?


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## ronboult (Oct 22, 2016)

Hi Bill
Did you ever find out what those two set screws are for?


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## scwhite (Mar 21, 2017)

wrmiller said:


> I have a Dorian BXA that I am putting on a 13" swing lathe and it has two pins that go into the t-nut. This I assume is to keep the tool post from twisting under load on heavier cuts, but is it really necessary on a 13" lathe? Reason I ask is that I cannot set to 29.5 (or any other angle for that matter) while it's pinned and I really don't want to have to remove the tool post (to remove the pins) to set an angle. Opinions welcome.


Take out the pins then use Red  Loctite on the threads into the tool post T-nut


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## Wreck™Wreck (Apr 7, 2017)

coolidge said:


> They use those QCTP on some CNC lathes Bill which can apply quite a lot of force, hence the video I posted recently of a QCTP twisting during a heavy cut and ripping the chuck off the lathe sending it flying at the operator's head. This whole 30 degree stuff I'm beginning to scoff at that. Sure if the ways and screws are sloppy. CNC lathes go straight at it and have no problem turning nice threads. I may just pin my QCTP and set it square.


Actually most controls have an approach angle setting in the canned thread cycle, the lathes that I have used default to 29.5 Deg., some have the option of cutting the left and right thread flanks alternately.

I have been threading on manual lathes for 30 years and have never used the compound other then for multiple start threads.


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