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Threading in reverse- PM 1236

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JPower6210

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#1
Hi Folks- not necessarily PM specific, but... I am starting to get into threading on on my lathe- This is all fairly new to me. Unfortunately, the project that I have on the lathe now requires a 11.5 TPI internal thread. I am planning on using 12 based on the fact that the PM won’t do 11.5 and leaving it a bit loose- it’s for a garden hose adapter so shouldn’t be an issue. I will be threading to a shoulder so I want to do it in reverse and thread towards the tailstock. Here is the piece I can’t seem to wrap my head around- If I run the tool on the backside, right side up with the feed headed towards the tailstock, will I still be cutting right hand threads. I plan on turning the compound 29ish degrees the opposite way from regular threading to cut on the leading face.

Am I missing anything? Thanks!

JP
 

digadv

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#2
You can get very close to 11.5 on this lathe ... this post shows all of the TPI possibilities.

https://www.hobby-machinist.com/threads/pm1236-qcgb-complete-thread-pitch-list.59034/

Also, you can turn the threading tool upside down and run the lathe in reverse going right to left. There are some youtube videos that show the process. While I would love to do this myself, my current indexable threading tool does not have the clearance needed to do this.
 

Karl_T

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#3
Running a tool upside down is problematic. You're pulling up with your cutting forces.

Run right side up but cut on the back side to do an ID thread in reverse. BTW, this is my preferred method for ID threads.
 

jbolt

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#4
Running a tool upside down is problematic. You're pulling up with your cutting forces.

Run right side up but cut on the back side to do an ID thread in reverse. BTW, this is my preferred method for ID threads.
Nothing wrong with using an inverted cutter for threading.

Sent from my SM-G955U using Tapatalk
 

WyoGreen

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#5
I found this video a while back which shows threading toward the tail-stock


Steve
 

digadv

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#6
Yes, that's the video I saw also. Meant to say left to right (towards the tail stock) in my previous post.

OP, let us know if you try this and how it works out.
 

JPower6210

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#7
All- thanks for the help! I finished this little project (Haralson Hose End from The Machinist Bedside Reader) last night. Works great for cleaning off my deck. This was a great project for a beginner with a number of operations. I used the change gears (44 and 38) which got me to a 11.515 TPI thread and used the 8 on the threading dial since that was indicated for all the 1/2 threads. I did it in reverse, using the method shown in the video above. Definitely was more relaxed than trying to disengage coming up to the shoulder. I plan on doing all of my internal threading this way. I was originally going to grind a tool for the process but ended up ordering the Mesa ID/OD Threading and Grooving tool which worked perfectly. I am planning on making a few more of these as gifts, and scaling down the internal measurements per Lautard to accommodate typical home water pressures.

JP
 

BaronJ

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#8
Hi Guys,

Be careful running the lathe in reverse if you have a thread mounted chuck, there is the danger of it unscrewing under load.
 

ttabbal

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#9
Hi Guys,

Be careful running the lathe in reverse if you have a thread mounted chuck, there is the danger of it unscrewing under load.
Always worth reminding. In this case, the lathe is a camlock chuck, so they are good to go.

Mine has the same mount and the reverse threading is super useful. Line up the thread dial, engage, release when you feel like it. :)
 
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