Chasing threads

[jocat54]

Well I learned how to chase some internal threads today....not nearly as hard as I thought it would be.

I was making a spindle thread protector for my SB9 and was about 3/4th's finished when my home made internal threading tool bent. My fault not watching what I was doing close enough. I made another tool out of some old sucker rod and a cheap import 1/4" bit. I drilled a 9/32nd hole in the sucker rod and used a small square file to make a square hole for the bit (really didn't take very long) and the drilled and tapped a set screw in the end to secure the bit. Worked really well.
Chasing the threads wasn't hard after I thought about it for while.

Engage back gear-engage half nuts on the right line-run the carriage under power into the hole-then use cross feed and compound to put the bit into the thread exactly--turn by hand to assure all was good-reset cross slide to zero-resume cutting threads (hardest part was trying to see the thread with the tool in the hole)

Turned out good!

 

[Ray C]

Cool deal...

I have a small mirror with a magnetic base attachment and sometimes use it to see inside the bore. Once in a while, I just put a piece of tape on the ways to know when to flip the lever. Also, it really helps to cut a recessed shoulder at the end of the thread. It helps visualize the stopping point and if you cut the shoulder the precise depth, when the bit first scratches inside it, you know when the proper thread depth is reached.

... Show us some pics of how it turned out.

Ray

 

[darkzero]

I have a small mirror with a magnetic base attachment and sometimes use it to see inside the bore. Once in a while, I just put a piece of tape on the ways to know when to flip the lever. Also, it really helps to cut a recessed shoulder at the end of the thread. It helps visualize the stopping point and if you cut the shoulder the precise depth, when the bit first scratches inside it, you know when the proper thread depth is reached.

Ray

I use a dial indicator with a magnetic back on ways for threading (internal & external). Analog is much easier to read (DRO is damn nearly impossible for me to read) when disengaging the halfnut at depth. I put the 0 mark at 12 o'clock.

For internal threading, I use my threading tool upside down & thread on the opposite side. Since the tool is upside down you still run the spindle in foward rotation. This allows at least some visibility for the internal thread on start & the compound can be set in the same position as you would cut external threads (if you thread with the modified flank method).

 

[Ray C]

Will,

Would you mind telling me the brand/model and insert style for that threading boring bar?


Thanks

Ray

 

[Tony Wells]

Let's see if I can describe this......like so may things, this takes far longer to type out than to actually do.

When I have an ID thread to chase (and sometimes I do this on an OD too), I mount everything up except the actual bar. I will run the spindle, engage the half nuts and when the toolholder is still safely away from the part, stop the spindle and just let it coast down. Making sure that there is room for the required threading bar length of course. Then I roll the cross feed until it is in a position that I know will be a bit shy in -X-when the bar is actually engaged, I slide the threading bar into the hole while letting it ride in the toolholder. I always use flat bottomed holders rather than bar holders. Then, using light finger pressure, I slip the insert (or tool steel) cutting point into an existing thread. This way, the butt end of the bar is touching only the far end of the tool holder and at a slight angle, touching the insert in one of the existing threads. Two points of contact only. One in the thread, one on the far end of the holder. Now keeping finger pressure on the bar, approximately midpoint between these two points, I crank the cross slide towards the centerline of the machine. The bar will straighten out, still be engaged in the thread, and at some point, be held against the back of the tool holder slot and disengaged from the thread. If this is done right, all you have to do is snug the set screws and you are timed with the thread. Of course, I always note the digital, or dial reading when I make contact with the back of the bar holder so I know approximately where the first cut should be. I back off that a bit and take a test cut, and if all is well, proceed to chase the thread.

Now how's that for confusing? I could have chased three threads by now!

Caution, I wrote this in a hurry, so if I missed a step, expect someone to call me out on it, or at least ask a clarification question.

 

[darkzero]

Will,

Would you mind telling me the brand/model and insert style for that threading boring bar?


Thanks

Ray

Sure Ray, my threading tools are made by Carmex. I thread 20 TPI the most so I use full profile 20 UN inserts, 11 IR 20 UN is on the internal bar pictured above & 16 ER 20 UN for my external holder. For the other common threads I cut I use partial profile A60 inserts which covers 16-48 TPI.

Picture below are the Carmex tools on AXA holders (with the A60 inserts) cause these are the tools I used on my 8x14 & I haven't had a need to upgrade them. The inserts last forever! In fact, I'm still on the first tip after 3 yrs & most of what I thread is Ti 6-4 & steels.

 

[Metalmann]

Nice threads.

I see you are making LED flashlights?

Powerful little buggers.