I needed to make a few treaded studs 2-56 for a model engine I'm building. The Machinery's Handbook tells me for a external thread , major diameter the max is .0854 and the min is .0813. I turned my stock to .082 and couldn't get the die to even begin to start. At .081 with die started cutting. Two questions: 1- Is the major diameter used only when single point cutting? 2- Is there a rule of thumb on how much smaller to turn material when using a die? Thanks for any light you can shine on this. Roger
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Threading with a die
- Thread starter rebush
- Start date
I just did a basic Google and found this chart.
http://www.carbidedepot.com/formulas-tap-standard.htm
Looks like the major Basic Major dia. is .086 and it says Basic effective diam is .0744. Many times when I tap holes I over size a hole so I don't break a tap, so you might turn the shaft down smaller to get an "effective" or easier to die/thread the part.
What material are you using, maybe practice on a softer material? Will your die thread onto a factory turned bolt? Is your die sharp? Using the correct end? To be honest I can't remember ever making a thread that small, but I have made 8/32 and I will file a bevel on the end to make it feed on easier. If your doing it in a lathe I will run the tail-stock up to it and insert the the center in the opposite end of the die to center the die on the bolt. I have also seen other machinist remove the center and press the tailstock barrel against it. Maybe on something that so small turn a small shaft with a short nipple and flat shoulder to put in your drill chuck / tailstock to center it in the bolt. You may also adapt the alignment shaft on a drill press and a very very small V-block.
http://www.carbidedepot.com/formulas-tap-standard.htm
Looks like the major Basic Major dia. is .086 and it says Basic effective diam is .0744. Many times when I tap holes I over size a hole so I don't break a tap, so you might turn the shaft down smaller to get an "effective" or easier to die/thread the part.
What material are you using, maybe practice on a softer material? Will your die thread onto a factory turned bolt? Is your die sharp? Using the correct end? To be honest I can't remember ever making a thread that small, but I have made 8/32 and I will file a bevel on the end to make it feed on easier. If your doing it in a lathe I will run the tail-stock up to it and insert the the center in the opposite end of the die to center the die on the bolt. I have also seen other machinist remove the center and press the tailstock barrel against it. Maybe on something that so small turn a small shaft with a short nipple and flat shoulder to put in your drill chuck / tailstock to center it in the bolt. You may also adapt the alignment shaft on a drill press and a very very small V-block.
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I'm not too familiar with smaller screws like that but generally, when using a die, I cut the stock just a couple thou less than major diameter but more importantly, bevel the leading edge about 45 degrees for the 1st 1 to 1-1/2 turns. On a lathe, I usually cut the stock about 3% (percent) less than major diameter because the metal deforms and increases in diameter quite a bit. FYI: On a store-bought bolt of 1/2" diameter, the threads typically measure .485 to .487. You'll find this to be the case with virtually all store-bought bolts. The outer edge of the threads do not contribute significantly to fastening strength. The bulk of the work is done by the center 50-75% of the thread area which is why many drill charts show engagement tables at 50 and 70%.
Finally, different dies come in various tolerance ranges denoted with H-x and B-x where X ranges from 1 to 5 usually and is measured in the ten-thousandths units. H is oversized (for when the bolt will be plated) and B is undersized (for very tight fit). Most store-bought dies aren't even marked but I believe they're typically in the low H range.
FWIW, when I'm tapping a hole where the depth is less than 1-1/2 times the bolt diameter, I use a drill bit one size smaller than what the 70% engagement calls for and I put a slight countersink of 1 to 1-1/2 turns depth so it starts easily. For hole depths greater than 1-1/2 times bolt diameter, I use the recommended bit for 70% engagement.
Ray
Finally, different dies come in various tolerance ranges denoted with H-x and B-x where X ranges from 1 to 5 usually and is measured in the ten-thousandths units. H is oversized (for when the bolt will be plated) and B is undersized (for very tight fit). Most store-bought dies aren't even marked but I believe they're typically in the low H range.
FWIW, when I'm tapping a hole where the depth is less than 1-1/2 times the bolt diameter, I use a drill bit one size smaller than what the 70% engagement calls for and I put a slight countersink of 1 to 1-1/2 turns depth so it starts easily. For hole depths greater than 1-1/2 times bolt diameter, I use the recommended bit for 70% engagement.
Ray
Richard: I was using brass. The die is new and I'm using the correct end. I made a holder for my die's that goes in the tailstock chuck so I should have near perfect alignment. The die will work on an existing bolt. Thanks for the link. Haven't heard of the effective diameter. Now I know how small I can go and still have threads. Seems like if I turn my material half way between the major dia. and the effective dia. that would be a good starting point. The problem with small threads is I turn to final size in one pass from larger stock. In this case I was using 3/8 material. Thanks again for your help. Roger