Internal Threading Setup ?

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michaelb
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Internal Threading Setup ?

Post by michaelb » Wed Jan 18, 2012 11:13 pm

I recently had done some internal RH threading using a RH tool holder with a laydown insert and although I got it done I figured I would explore using a LH tool holder and go from chuck to tailstock. I first looked at the threading charts from the manufacturers and determined that to thread the Int RH thread with a LH bar that I would need to go with a reverse helix. I understand the logic however when I looked at some Vardex bars I see that in the smaller size shanks (less than 1 inch or so) that they do not come with anvils. I am looking to find a bar that will accomodate a 3/8 IC insert and be able to thread to a minimum of a hole .625 or so. Anybody on here have much experience with threading in this manner with similar requirements ? I know that I can grind some HSS but would like to have the insert option if it is available.


Mike

tetramachine
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Re: Internal Threading Setup ?

Post by tetramachine » Sat Jan 28, 2012 7:20 pm

I do a fair amount of internal threading. I use Micro 100 threading tools, these are solid carbide not inserts. large range of thread with just a couple bars. The relief allows cutting a RH or LH thread with the same tool. They are always on ebay, i try to buy when they are in lots of 2-3 bars. They can be touched up with a diamond wheel, if you break one, save it and grind a special profile for those little cleanup jobs. I'd suggest if you buy one also buy the holder, these a 1/2" d cylinders that I leave in the QCTP holder all the time and just swap bits, so first the boring bar, swap to the chamfer bar, then a thread relief bar, then the threading bar. Stick with a cutting lenght of .8-1.25 that should cover most depths you need for single point threads. Generally I single point all the left hand and stuff larger than 1/2" and then there are the oddballs 11/16-24, 7/8-36.
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Dave_C
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Re: Internal Threading Setup ?

Post by Dave_C » Sat Jan 28, 2012 10:09 pm

Mike,

5/8" hole is pretty small but I think there may be some bars that will go that diameter. Option is just buy a 5/8" bottoming tap and thread it. (?)

I have used my small HSS tool to do internal threads, not sure I went that small. I do like the headstock to tail stock approach to internal threading as I don't have to use an indicator to stop at the bottom of the hole.

Just make sure you turn you compound so that you are drawing the threading tool into the helix as you thread and not away from it. (Leading helix toward the tailstock as you run in reverse)

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tetramachine
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Re: Internal Threading Setup ?

Post by tetramachine » Sun Jan 29, 2012 4:18 pm

The way to make it easier to RH thread in a blind hole is to cut a thread relief at the point you want the threads to end. When using carbide inserts or solid bar threading tools, it is very important to not overrunn the previous cut threads, as it instantly breaks the tip off the tool. That awful crunch sound. A thread relief is just a groove cut as deep as the depth of the thread, and about 2 pitches wide. A precut thread relief then as a tapered portion as well, maybe a couple pitches long. If your cutting a 5/8" thread normal thread lenght would be 1.5 x diameter, so 15/16 deep.

So you have cut your thread relief, you now set your threading tool, and measure 15/16 up the lenght of the threading tool, black marker the position on the tool. Now take your first cut and listen, when the sound of the tool as it cuts, stops, release the half nuts, take the black marker out and mark a line on the ways at the end of the carriage at the headstock end. Now you will be feeding out with the compound so the mark on the cutter will move relative to the work, but the line on the ways carriage will remain the same, and you can listen as well.

Some guys forget to move the compound to the other side of the crosslide, It cutting works so much better when its advancing the cutter than retracting the cutter.
Last edited by tetramachine on Sun Jan 29, 2012 5:00 pm, edited 1 time in total.
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Harold_V
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Re: Internal Threading Setup ?

Post by Harold_V » Sun Jan 29, 2012 4:57 pm

tetramachine wrote: A thread relief is just a groove cut as deep as the depth of the thread pitch,
It should be noted that the relief diameter would be machined to the theoretical major diameter of the thread, not the pitch diameter. Starrett conveniently marks the double depth of threads on their fishtail gauges.
Some guys forget to move the compound to the other side of the crosslide, It cutting works so much better when its advancing the cutter than retracting the cutter.
The compound should ALWAYS be set so that feed is in the same direction as carriage travel when cutting the thread. For an internal thread, RH, assuming cutting towards the headstock, the compound should be set at either 7:00 or 1:00.

Harold
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michaelb
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Re: Internal Threading Setup ?

Post by michaelb » Mon Jan 30, 2012 8:52 pm

Thanks for all the tips, Dave, Harold and tetramachine. I was not so much concerned with the threading in the blind hole as much I was curious to find out if using inserts and threading RH intenal threads in a LH holder if bars were readily available with the option of changing anvils to obtain the correct geometry. When I was looking at Vardex products it seemed that many of their LH holders did not come with the anvil option and apparently the relief (1.5 degrees) was machined into the tool insert seat.

I think that I abandoned that thought anyway for now as I have a threaded spindle and not sure if it would be a wise idea even at low speed with a light cut. It is a hit and miss situation when I thread into a blind hole and have heard the distinct sound of "CRUNCH" one too many times, relief was just not wide enough and did not have the room to make it wide enough.

Still thinking on the problem and filed it away with all the other ones I have in mind.


Mike

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GlennW
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Re: Internal Threading Setup ?

Post by GlennW » Mon Jan 30, 2012 10:18 pm

michaelb wrote: It is a hit and miss situation when I thread into a blind hole and have heard the distinct sound of "CRUNCH" one too many times, relief was just not wide enough and did not have the room to make it wide enough.
Set up a dial indicator as well as the Sharpie marks on the tool shank or bed way when internal threading to a shoulder. Set the indicator so that you have only one revolution of the dial to your stopping point. Tat way you won't loose count of revolutions and you will have plenty of time to get the half nuts disengaged prior to hitting the shoulder. Keep in mind that as you advance the compound, providing that it is set to about 29 degrees, the toool will advance toward the shoulder, so take that into account when setting up. I'll bet you will find that you can stop within a few thousandths of your zero mark on every pass if you are paying attention.

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