Internal Threading Tool ?

michaelb · Post by **michaelb** » Tue Dec 01, 2009 9:10 pm

Looking for some feedback on an idea for an internal threading tool. Need to thread some 15/16-16 threads in a 1" block of aluminum for a ballnut mount. Not done much threading on the lathe but it seems that all the insert tooling that I see is pretty pricey, at least for someone like myself to only use occasionally. So I am thinking of grinding a HSS bit and mounting it perpendicular in a small bar that would mount in the tool holder.

Also, do I feed from the headstock to the tailstock on the backside or the front side of the nut ?

Any and all thoughts on this approach would be appreciated.

Thanks

Mike

dly31 · Post by **dly31** » Tue Dec 01, 2009 9:30 pm

You can feed in either direction in either position. It just depends on whether you are turning a right or left hand thread and whether the lathe chuck is turning in the normal or reverse direction. For a right hand thread, the common method is with the chuck turning normally and feeding toward the headstock with the tool at the front. If you are afraid of bottoming out the tool, you can reverse the chuck and feed out.

Since it is hard to see what you are doing that way, some like to thread at the back with the chuck turning backward and feeding toward the tailstock.

If your chuck threads on, be sure it is tight and be careful it does not un-screw if you turn it backwards. If you are unsure of yourself, practice on some scrap, preferably with a good sized hole to get the hang of it. Just be sure you do not cut a left-hand thread by mistake, and be careful not to jam the tool into the bottom of the hole or the chuck!

Don Young

michaelb · Post by **michaelb** » Tue Dec 01, 2009 10:23 pm

Thanks for the tips on the threading. As soon as I posted the feed question I realized that the feed would correspond to RH/LH. Not done much threading on the lathe.

About the only threading attempt that I have done did not work out all that well. I had attempted to do some external threads on a piece of 1018 with a HSS bit I ground and the threads came out looking pretty nasty. Was not all that fun trying to grind the thread profile on the bit either.

Any thoughts on an internal threading tool that would do at least a 1" depth ?

My first thought was to just pick up an insert threading tool holder but when I seen what they cost, I could not justify the expense for cutting just a couple threads. Then again, it almost seemed like major research just looking at all the different styles in the Enco catalog.

Mike

mechanicalmagic · Post by **mechanicalmagic** » Tue Dec 01, 2009 11:03 pm

Grinding tool bits and threading seem to be the great mystery for newcomers. Trust me, it's very easy. A little practice is all it takes.

BTW, where in CA are you?

Dave J.

JimGlass · Post by **JimGlass** » Tue Dec 01, 2009 11:12 pm

Mike;

I made ballnut mountings a few weeks ago. I used a tool like the first or second tool shown. I made those tools myself on my surface grinder. They can also be hand ground.

Ballnut mounting

Jim

mechanicalmagic · Post by **mechanicalmagic** » Tue Dec 01, 2009 11:29 pm

Jim,
And others, the server has gone berzerk. It seems to refuse the post, but actually doesn't. I found a new button, it was able to delete my entire (duplicate) post. But it was only visible on a double post.

Dave J.

JimGlass · Post by **JimGlass** » Tue Dec 01, 2009 11:43 pm

Thanks Dave;

I was unable to find a way to delete my double post.

My bed time anyway;

Jim

tailshaft56 · Post by **tailshaft56** » Tue Dec 01, 2009 11:56 pm

Same error here. Just did the same as MM.

Post by **Harold_V** » Wed Dec 02, 2009 12:34 am

dly31 wrote:Since it is hard to see what you are doing that way, some like to thread at the back with the chuck turning backward and feeding toward the tailstock.

It should be noted that the position of the compound is very important. When chasing threads, if the compound feeds in the opposite direction of travel when the tool is cutting, you risk tool pressure pushing the tool away from the material. The end result is a drunken thread, which may measure properly regards the pitch diameter, but likely won't function as expected because of the irregular lead.

Rule of thumb, and it applies regardless of the thread type, be it internal or external, running forward, or reverse, cutting left hand threads, or right hand threads. The angle setting of the compound should be no greater than the half angle of the thread, with a slightly lesser angle chosen (½ to 1° less), and the compound should feed in the same direction that the carriage travels in the cut. There are no exceptions aside from a square thread.

Harold

tornitore45 · Post by **tornitore45** » Wed Dec 02, 2009 1:56 pm

Also consider the side clearance must be increased by the lead angle on the cutting side, consistent with the handness/direction/and OD vs. ID.

david5605 · Post by **david5605** » Wed Dec 02, 2009 2:50 pm

You can also practice threading on a chunk of heavy wall PVC pipe or even a pvc coupling till you get your confidence up. Cheap way to not worry about crashes destroying the work or cutter.

tmc_31 · Post by **tmc_31** » Wed Dec 02, 2009 3:48 pm

Michaelb,

I am very new to this machining stuff so please take what I say with a grain of salt.

I battled the internal threading demon a few weeks ago and found that, like many machining operations new to me, internal threading is not the bear it presents itself to be. Just try it! Practicing on a piece of PVC is a good idea.

I needed to turn a 1 1/4"-20 TPI thread in a piece of 1 1/2" DOM Tubing about 1" deep on a collet closer project. I used a 5/8" boring bar that came with my lathe. It is about 12" long and has a 90 deg 1/4" square hole in one end and an angled hole of the same size in the other. I held the boring bar as short as I could in the tool holder to minimize spring in the boring bar. I ground a 1/4" tool bit from a 2" HSS blank. I had made a guide out of scrap steel to help me get the 60 deg angle right. I inserted the HSS bit into the tool bar with about 3/8" sticking out on the thread cutting side. I then cut off the back of the tool blank flush with the boring bar. I used another smaller boring bar with a standard lathe (1/4") HSS bit to carve the ID of the tubing out to the minor diameter of the thread that I was cutting. Then I cut a thread relief groove about 1" deep into the tube to the depth of the major diameter. The relief groove was about 1/4" long. I then proceeded to cut the threads in the normal manner with the tool moving toward the headstock and the top of the tubing rotating towards me. I could hear the cutter move into the relief groove and so knew when to disengage the half-nuts. When I got close to the final depth, I started taking light passes (.002 or so) and using the threaded end of a 5C collet as a plug gage.

All in all it worked out pretty good, the threads were a little ragged (I cut these threads dry, I will use thread cutting oil on the next ones) but I was able to clean them up with a light pass of a die grinder and the judicious application of a wire wheel. It was a great learning experience as I had a lot of excellent advice from posters on this forum and others.

All the best,

Tim