In my recent topic on threading a 3/4 x 10 hole, threadmills were
suggested. many brought up using a hand made unit.

My question is how much smaller the thread mill needs to be than the
bore. Picture the worst case, if the thread mill is the same size as
the bore, it will just bore out the hole with no threads at all. Looks
to me as if a thread mill 90% of the bore size would leave a very flat
thread form. the math on this is way above my pay grade.

I'm looking to my winter project. making a custom RPD receiver. I
bought a 15mm x 1.5mm thread mill to make a 24 x 1.5 barrel thread.

Karl

On Sun, 06 May 2012 07:38:22 -0500, Karl Townsend
wrote:

In my recent topic on threading a 3/4 x 10 hole, threadmills were
suggested. many brought up using a hand made unit.

My question is how much smaller the thread mill needs to be than the
bore. Picture the worst case, if the thread mill is the same size as
the bore, it will just bore out the hole with no threads at all. Looks
to me as if a thread mill 90% of the bore size would leave a very flat
thread form. the math on this is way above my pay grade.

I'm looking to my winter project. making a custom RPD receiver. I
bought a 15mm x 1.5mm thread mill to make a 24 x 1.5 barrel thread.

Karl
The thread mill needs to be smaller than the minor diameter. You
should program with cutter compensation so you can easily change the
P.D.

"Karl Townsend" wrote in message
...
In my recent topic on threading a 3/4 x 10 hole, threadmills were
suggested. many brought up using a hand made unit.

My question is how much smaller the thread mill needs to be than the
bore. Picture the worst case, if the thread mill is the same size as
the bore, it will just bore out the hole with no threads at all. Looks
to me as if a thread mill 90% of the bore size would leave a very flat
thread form. the math on this is way above my pay grade.

I'm looking to my winter project. making a custom RPD receiver. I
bought a 15mm x 1.5mm thread mill to make a 24 x 1.5 barrel thread.



This is why I suggested chasing with a tap.

Karl Townsend wrote:

In my recent topic on threading a 3/4 x 10 hole, threadmills were
suggested. many brought up using a hand made unit.

My question is how much smaller the thread mill needs to be than the
bore. Picture the worst case, if the thread mill is the same size as
the bore, it will just bore out the hole with no threads at all. Looks
to me as if a thread mill 90% of the bore size would leave a very flat
thread form. the math on this is way above my pay grade.

I'm looking to my winter project. making a custom RPD receiver. I
bought a 15mm x 1.5mm thread mill to make a 24 x 1.5 barrel thread.
The threadmill needs to safely clear the minor thread diameter so
it won't gouge the opposite wall while milling the thread, and also
can be removed from the completed bore. For large bores like your
3/4", it can probably be quite a bit smaller. All it needs is to have
enough tooth extending from the shaft to cut the thread.

A single-row threadmill is orbited around the bore as many times as there
are partial and complete threads in the bore depth.

A full threadmill is orbited only one turn plus a little bit.
They are generally plunged through the hole at the XY center and
then orbited counterclockwise up the hole to make the cut in the
climb-mill direction.

Jon

On Mon, 07 May 2012 11:48:58 -0500, Jon Elson
wrote:

Karl Townsend wrote:

In my recent topic on threading a 3/4 x 10 hole, threadmills were
suggested. many brought up using a hand made unit.

My question is how much smaller the thread mill needs to be than the
bore. Picture the worst case, if the thread mill is the same size as
the bore, it will just bore out the hole with no threads at all. Looks
to me as if a thread mill 90% of the bore size would leave a very flat
thread form. the math on this is way above my pay grade.

I'm looking to my winter project. making a custom RPD receiver. I
bought a 15mm x 1.5mm thread mill to make a 24 x 1.5 barrel thread.
The threadmill needs to safely clear the minor thread diameter so
it won't gouge the opposite wall while milling the thread, and also
can be removed from the completed bore. For large bores like your
3/4", it can probably be quite a bit smaller. All it needs is to have
enough tooth extending from the shaft to cut the thread.

A single-row threadmill is orbited around the bore as many times as there
are partial and complete threads in the bore depth.

A full threadmill is orbited only one turn plus a little bit.
They are generally plunged through the hole at the XY center and
then orbited counterclockwise up the hole to make the cut in the
climb-mill direction.

Jon

OK, thanks everybody. Sounds like I'm guilty of over thinking
something. I'm going to add single point thread milling to my list of
skills.

Karl

On May 7, 3:47*pm, Karl Townsend
wrote:
On Mon, 07 May 2012 11:48:58 -0500, Jon Elson
wrote:









Karl Townsend wrote:

In my recent topic on threading a 3/4 x 10 hole, threadmills were
suggested. many brought up using a hand made unit.

My question is how much smaller the thread mill needs to be than the
bore. Picture the worst case, if the thread mill is the same size as
the bore, it will just bore out the hole with no threads at all. Looks
to me as if a thread mill 90% of the bore size would leave a very flat
thread form. the math on this is way above my pay grade.

I'm looking to my winter project. making a custom RPD receiver. I
bought a 15mm x 1.5mm thread mill to make a 24 x 1.5 barrel thread.
The threadmill needs to safely clear the minor thread diameter so
it won't gouge the opposite wall while milling the thread, and also
can be removed from the completed bore. *For large bores like your
3/4", it can probably be quite a bit smaller. *All it needs is to have
enough tooth extending from the shaft to cut the thread.

A single-row threadmill is orbited around the bore as many times as there
are partial and complete threads in the bore depth.

A full threadmill is orbited only one turn plus a little bit.
They are generally plunged through the hole at the XY center and
then orbited counterclockwise up the hole to make the cut in the
climb-mill direction.

Jon

OK, thanks everybody. Sounds like I'm guilty of over thinking
something. I'm going to add single point thread milling to my list of
skills.

Karl

It does need to be some percentage smaller or you will end up thinning
your thread. I don't know offhand how much that is, but you should be
able to find the information in a catalog. I seem to remember old
Seco catalogs specifying the minimum diameter that could be cut with a
cutter/insert combination. Hopefully which ever company you order
from will have the data.

If the concept of thread thinning isn't intuitive, I guess that the
best example I can think of offhand is this - Picture the helical
groove being unwrapped and placed as a slanted v-groove climbing a
flat wall. Then to exaggerate, picture a ten inch diameter v-form
cutter following that trajectory. The cutter has the right form, but
since the spindle axis isn't normal to the groove being cut the cutter
will gouge.

On Tue, 8 May 2012 16:02:23 -0700 (PDT), MadHatter
wrote:

On May 7, 3:47*pm, Karl Townsend
wrote:
On Mon, 07 May 2012 11:48:58 -0500, Jon Elson
wrote:









Karl Townsend wrote:

In my recent topic on threading a 3/4 x 10 hole, threadmills were
suggested. many brought up using a hand made unit.

My question is how much smaller the thread mill needs to be than the
bore. Picture the worst case, if the thread mill is the same size as
the bore, it will just bore out the hole with no threads at all. Looks
to me as if a thread mill 90% of the bore size would leave a very flat
thread form. the math on this is way above my pay grade.

I'm looking to my winter project. making a custom RPD receiver. I
bought a 15mm x 1.5mm thread mill to make a 24 x 1.5 barrel thread.
The threadmill needs to safely clear the minor thread diameter so
it won't gouge the opposite wall while milling the thread, and also
can be removed from the completed bore. *For large bores like your
3/4", it can probably be quite a bit smaller. *All it needs is to have
enough tooth extending from the shaft to cut the thread.

A single-row threadmill is orbited around the bore as many times as there
are partial and complete threads in the bore depth.

A full threadmill is orbited only one turn plus a little bit.
They are generally plunged through the hole at the XY center and
then orbited counterclockwise up the hole to make the cut in the
climb-mill direction.

Jon

OK, thanks everybody. Sounds like I'm guilty of over thinking
something. I'm going to add single point thread milling to my list of
skills.

Karl

It does need to be some percentage smaller or you will end up thinning
your thread. I don't know offhand how much that is, but you should be
able to find the information in a catalog. I seem to remember old
Seco catalogs specifying the minimum diameter that could be cut with a
cutter/insert combination. Hopefully which ever company you order
from will have the data.

If the concept of thread thinning isn't intuitive, I guess that the
best example I can think of offhand is this - Picture the helical
groove being unwrapped and placed as a slanted v-groove climbing a
flat wall. Then to exaggerate, picture a ten inch diameter v-form
cutter following that trajectory. The cutter has the right form, but
since the spindle axis isn't normal to the groove being cut the cutter
will gouge.

You're right on. I thought this up on my own, but didn't know the
name. I won't be finding the exact info where i shop - fleabuy and
local auctions. I must have close to one hunder threadmills right now.
An auctioneer called them tap and i got a whole drawer for the opening
bid of $100.I've got watches on feabay to complete my set.

I don't have 10 TPI, just what i needed for the last job.
Karl