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 a
5x40 & 6x40.

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

In article 1119705063.093562.181590
@g47g2000cwa.googlegroups.com,
says...
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 a
5x40 & 6x40.

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



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

wrote in message
oups.com...
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 a
5x40 & 6x40.

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


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

wrote in news:1119705063.093562.181590
@g47g2000cwa.googlegroups.com:

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 a
5x40 & 6x40.

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


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.

--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

http://www.machines-cnc.net:81/

I see that several other people answered the question you asked,
however as a suggestion. You may want to take a look at guiding
the tap off the shank and not off the threads. Several
commercial tap guides are available using this approach, and this
avoids problems with tap wear, limits [i.e.H2 v h3, etc.]

On 25 Jun 2005 06:11:03 -0700, wrote:

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 a
5x40 & 6x40.

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

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

"Anthony" wrote in message
...
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.

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

http://tinyurl.com/aqrg5

Regards,

Robin

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

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