thread cutting from the sholder

JT.

JT.

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do i use a lefthhand thread cutting tool ore a innerthread cutting tool
bought up side down and with reverse feed and reverse backward rotation
i wand to do it that way i got a metric machine powered with a vfd (mono to 3phase V)so it has no stopping power
to make the machine stop frrom +250 rpm to stop in 2-3 rotations with the feed still engaged
and with carbit inserts i do not got good finish at low speeds
 
If I understand your plight, I think you need a standard threading tool, used upside down, near the chuck end, in the relief. You will need to turn the spindle in reverse. Not generally recommended for threaded-on chuck systems. Once you engage the half-nuts, leave them. Jog the spindle forward to get back to the relief. In fact, if you can, jog past it and then, moving away from the chuck, jog until you get to the relief, then set your -X- position for each cut. Repeat as necessary.
 
Definitely a right-hand threading tool, (clearance angles) either upside down on the side closer to you or right way up on the far side, tumbler reverse in right-hand-threading position, spindle in reverse. As Tony says, take up the slack before the tool engages by running to the "far" side of the run-in groove when you return to the start position.

Are you using carbide because the material you're threading is extra hard, or to save grinding a threading tool from HSS? As you've found, carbide needs high speeds and a rigid machine, HSS will generally give better results at lower speeds on lighter (sub-ton) machines.

I'm surprised you can't. et a fast enough stop, is your VFD programmed for dynamic or.D.C. Braking? I've added.a.brake resistor to mine (25 quid.on.eBay) and it stops *very* quickly, well within the runout groove. My lathe also has a clutch/brake between motor and gearbox, but I've found the.VFD braking more consistent. YMMV....
 
As already mentioned, HSS will provide a much better surface finish on light machines, especially when threading. Carbide should be used only be used if the material being cut is too hard for HSS or you are making many like parts as in production.

Another trick I've used when threading to a shoulder is to shut the spindle off with the half nut engaged and turn the chuck by hand to finish the thread. Don't try that with carbide though as that will chip the tool.

Tom
 
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British Steel said:
Definitely a right-hand threading tool, (clearance angles) either upside down on the side closer to you or right way up on the far side, tumbler reverse in right-hand-threading position, spindle in reverse. As Tony says, take up the slack before the tool engages by running to the "far" side of the run-in groove when you return to the start position.

Are you using carbide because the material you're threading is extra hard, or to save grinding a threading tool from HSS? As you've found, carbide needs high speeds and a rigid machine, HSS will generally give better results at lower speeds on lighter (sub-ton) machines.

I'm surprised you can't. et a fast enough stop, is your VFD programmed for dynamic or.D.C. Braking? I've added.a.brake resistor to mine (25 quid.on.eBay) and it stops *very* quickly, well within the runout groove. My lathe also has a clutch/brake between motor and gearbox, but I've found the.VFD braking more consistent. YMMV....
Click to expand...

To do a left hand thread at the back side of the bore don't you need a left hand tool right side up and the spindle reversed? Never did it so I'm asking not telling.
 
I don't think I would want to be doing ANY threading to a shoulder on a manual machine at 250 RPM's - forward, reverse, right or left hand.

I agree with the others, slow it down and use HSS. And as Tom said, don't be adverse to turning the spindle manually (no power). This can be done by adding a crank or wheel to the spindle fairly easily.

Good luck!
 
epanzella said:
To do a left hand thread at the back side of the bore don't you need a left hand tool right side up and the spindle reversed? Never did it so I'm asking not telling.
Click to expand...

Wwhatever direction you make the cut in, the.clearance angles are dictated by the thread handedness, so yes, a left-hand tool.

Assuming your lathe has a tumbler.reverse (or other leadscrew reverse), a left-hand thread will cut away from the.chuck in forward spindle, so not a.lot of point in reversing the spindle rotation....

Using a tool upside.down at the back of.a.bore is.a.good.idea anyway, as it gives a much better view of.the.action, but isn't essential, helps if.you have a carriage stop set.for.the bottom of.the bore, too!
 
Turning the chuck by hand in tricky situations is sound advice. Ian Bradley,in his book "The Amateur's Workshop", made a crank that fit into the outboard end of the spindle hole of his Myford lathe. It had an expanding plug that went into the hole in the spindle to keep the crank from slipping. A good accessory to have,if your lathe has a short enough headstock that you can reach the crank,and still see the cutter's exact position.
 
British Steel said:
Wwhatever direction you make the cut in, the.clearance angles are dictated by the thread handedness, so yes, a left-hand tool.

Assuming your lathe has a tumbler.reverse (or other leadscrew reverse), a left-hand thread will cut away from the.chuck in forward spindle, so not a.lot of point in reversing the spindle rotation....

Using a tool upside.down at the back of.a.bore is.a.good.idea anyway, as it gives a much better view of.the.action, but isn't essential, helps if.you have a carriage stop set.for.the bottom of.the bore, too!
Click to expand...
I would like to cut away from the shoulder with the tool right side up at the back of the bore for both left and right hand threads but between reversing the spindle, reversing the feed, reversing the tool and doing left or right thread, I'm getting pretty screwed up. My machine only goes down to 70 rpm so a shoulder in a hole scares me. I suppose I could hash this out on some scrap but I'd like to learn all I could from more experienced guys first as it may help me avoid breaking a tool.
 
Couple thoughts... Tony W. and others pretty much summed up what to do. Nelson (the site owner) once posted a very nice image of all the possible configurations of thread cutting (inside, outside, left, right etc). I'm looking for it but if anyones else can beat me to the punch, that's great.

Someone mentioned the desire to use carbide inserts but does not get good results at low speeds.... Here's a solution to that problem: I discovered these "Carmex brand" inserts on eBay and they are great. The have an extreme positive top rake and will cut anything at just about any speed from slow to fast. These inserts can run about 1/3 the RPM of normal thread cutting speeds and still do fine. I love them on stainless steel -they just don't seem to wear out.

BTW: If you purchase these items through eBay, ask for a fellow name Avi and mention this website. You might get a little deal on shipping... This place sells all kinds of boring bars too.

http://www.ebay.com/itm/10-Pcs-Carm...ultDomain_0&hash=item3ccdeb2fa4#ht_1509wt_907


Ray
 
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