PDA

View Full Version : Upside down tool holders ?



Boucher
05-19-2009, 10:50 AM
These have been mentioned in threads on Rear mounted cutoff tools and on threading up to a shoulder. I would like to make one as mentioned in a thread on PM "made an upside down tool holder (ya gotta use a left hand insert) and run the lathe backwards -- set up just like normal but you start the threads at the shoulder and run off the end of the barrel." I am having difficulty visualizing this. My lathe is a Nardini TT-1230E with a Dorian Quick change tool post. Making a dedicated tool holder for direct attachment to the cross slide would be OK if this would not work with the Quick change post. My brain is locked on Top Dead Center and I can't seem to get started on this. Any assistance would be appreciated.

lakeside53
05-19-2009, 11:50 AM
Maybe i'm missig something. Usually, I just mount the tool inverted in the holder.

If the tooling doesn't work being flipped, I just take the top adjust screw out of my Phase 2 QC holder, and flip the entire tool holder upside down... and adjust by hand before clamping.

TGTool
05-19-2009, 12:09 PM
Yup, same thing. If I've got a threading tool in a boring bar, for normal threading the insert will be pointing to the front. If I rotate the bar 180 degrees, the insert will be pointing to the back side of the lathe and upside down. It's still cutting in the same direction though, and I sometimes use this for ID threading since it keeps my compound swung in the same direction as OD threading and the retract is still in the same direction. This helps to keep from confusing the reflexes if I'm threading to an inside shoulder and have to whip several things at once (disengage half nut and retract tool).

With this upside down bar, now if I reverse the insert so it's again pointing to the front, the spindle rotation has to be reversed for the insert to cut and I would start a right hand thread from the inside and come out as in unscrewing a male thread from a nut.

Boucher
05-19-2009, 01:51 PM
I guess that I am the one that is missing something. If you invert the tool holder didn't it move off centerline by twice the thickness of the tool holder? I didn't think that there was enough height adjustment. I will go to the shop and try it. Thanks !

kmccubbin
05-19-2009, 03:10 PM
you're on the verge of 'getting it'. The trick is to run the spindle backwards, so the thread is cut while 'unthreading'. Then, since the work is going backwards, you need to either move the tool to the rear OR turn the cutter upside down. The cutting edge still needs to be on center, so you'll need to raise the toolholding block to compensate for the height difference. It's simple once you wrap your mind around it, and it makes threading a joy. I get a better surface finish this way, since it allows me to run a much faster SFPM.

Kerry