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drill bushing for tap help

I am building a jig to drill and tap a series of holes. In operation, the jig will have slip fit style drill bushings. I will drill the pilot hole, then run a tap thru the hole. I was planning to use a drill bushing that fits the thread cutting end of the tap, but don't have all the taps that I am going to need yet, so I do not have a way to check what size of drill bushing will fit the tap properly. The sizes I will be using are:

5x40 & 6x40.

Does anyone know of a formula, or real world answer to this question? TIA, ron

Reply to
rbce2003
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Machinery's Handbook shows the major diameter of taps in the "Taps and Threading Dies" section. The major dia of a

5-40 ground thread tap is .1275/.1265, 6-40 is .1405/.1395

Ned Simmons

Reply to
Ned Simmons

The formula for numbered screw sizes is the size times .013 plus .060. So, a 5-40 would be (5 x .013) + .060 or .125. A tap will be a couple thou bigger than the screw.

Jerry

Reply to
Jerry Foster

snipped-for-privacy@hotmail.com wrote in news:1119705063.093562.181590 @g47g2000cwa.googlegroups.com:

Be aware that the tap drill for the screw will be smaller than the tap, so if you use bushings that allow the tap to go through, they will be loose on the drill. This leads to the question: Are you using the bushings to locate the holes, or are you using them to make sure the tap is square to the material? You can't have both without changing bushings.

Reply to
Anthony

Reply to
F. George McDuffee

Thanks for the help, quite timely.

Jerry & Ned: Spot on advice, chaps.

Anthony: I am using different bushings for the drill and tap

F. George McDuffee: you have a very good point. I just do not have the real estate in the jig to accomodate that.

I have another quiery: I found the spot mentioned about clearance hole dimensions for common taps in Machinist Handbook... my next question would be if anyone can help me with finding the same dimension for HELI-COIL taps?

thanks again, ron

Reply to
rbce2003

I think he's going to use slip renewable bushings (or should). Much easier than building another jig for a secondary operation....

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Regards,

Robin

Reply to
Robin S.

Yes indeed Robin S. ... slip renewable bushings are being used. PS great link! Lots of neat stuff there, ron

Reply to
rbce2003

Yes indeed Robin S. ... slip renewable bushings are being used. PS great link! Lots of neat stuff there, ron

Reply to
rbce2003

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