What drill size for M8x1.0 6H form tap?

Finegrain · Dec 8, 2018

Hi guys,

I actually can't find the recommended drill size for M8x1.0 6H. Neither the Balax website, my big wall chart, nor MHB seem to give this info.

This is M8x1.0, not the standard M8x1.25.

If I had to guess, following the pattern of M6x1.0 and M7x1.0, I'd say 7.5mm, but that's just a guess.

Thanks, and regards.

Mike

pablo.casiano75 · Dec 8, 2018

I would just measure the threads minor diameter and go from their. Form tap drill sizes are always bigger so yeah just measure your taps minor dia . and choose the closest drill size. Maybe go a couple thousands smaller, no more than . 005 . Hope this helps. [emoji846]

Sent from my Pixel 2 using Tapatalk

Newman109 · Dec 8, 2018

Finegrain said:
Hi guys,

I actually can't find the recommended drill size for M8x1.0 6H. Neither the Balax website, my big wall chart, nor MHB seem to give this info.

This is M8x1.0, not the standard M8x1.25.

If I had to guess, following the pattern of M6x1.0 and M7x1.0, I'd say 7.5mm, but that's just a guess.

Thanks, and regards.

Mike

Hello,
Oops, my wall chart doesn't quote size for an 8X1 form tap, but you knew that. LOL.

litlerob1 · Dec 8, 2018

It's usually just guessing for me anyway. I expect to drill and tap a couple holes in scrap first, to get the minor diameter right anyway. But I would agree with your thinking. IT also depends on the material; Aluminium is going to displace a lot more than cast Iron.

R

DanielG · Dec 8, 2018

Guhring say 7.520 - 7.620 for their M8x1.0 form tap. Class is 6HX.

Finegrain · Dec 8, 2018

DanielG said:
Guhring say 7.520 - 7.620 for their M8x1.0 form tap. Class is 6HX.

Perfect, thanks!

Regards.

Mike

Bobw · Dec 8, 2018

pablo.casiano75 said:
I would just measure the threads minor diameter and go from their. Form tap drill sizes are always bigger so yeah just measure your taps minor dia . and choose the closest drill size. Maybe go a couple thousands smaller, no more than . 005 . Hope this helps. [emoji846]

Sent from my Pixel 2 using Tapatalk

That's a good way to end up with a broken tap..

General rule of thumb. Pitch diameter plus a little.

8mmx1 with a PD of 7.35mm to 7.5mm would be a drill of around 7.5mm or a bit bigger...

lets go to imperial.. 1/4-28 is an A.. .234... PD of a 1/4-28 is .226-.231.

Same rule applies for thread rolling.. PD minus a little.

And get yourself some ME ThreadPal.. Best $100 you'll ever spend as a machinist.. I put
off buying it for years, and when I finally did buy it, it paid for itself in just a few weeks.
I never had to Google the drill size for a form tap... I didn't have to calculate any wire sizes,
I didn't have to find a Machinery's Handbook... Didn't have to try and figure out where I left
that damn J-thread spec this time. It made pipe threads and Acme threads a breeze.

Its made and sold by member here... And I'm not affiliated, just a happy customer.

guest · Dec 8, 2018

I use a 19/64 drill for M8x1 form taps.

pablo.casiano75 · Dec 8, 2018

Yeah but if you use the pitch dia. He will have no threads. He needs to measure the minor dia.. , everyone does things differently but just trying to help. I'm sure someone will know the exact drill size.

Bobw said:
That's a good way to end up with a broken tap..

General rule of thumb. Pitch diameter plus a little.

8mmx1 with a PD of 7.35mm to 7.5mm would be a drill of around 7.5mm or a bit bigger...

lets go to imperial.. 1/4-28 is an A.. .234... PD of a 1/4-28 is .226-.231.

Same rule applies for thread rolling.. PD minus a little.

And get yourself some ME ThreadPal.. Best $100 you'll ever spend as a machinist.. I put
off buying it for years, and when I finally did buy it, it paid for itself in just a few weeks.
I never had to Google the drill size for a form tap... I didn't have to calculate any wire sizes,
I didn't have to find a Machinery's Handbook... Didn't have to try and figure out where I left
that damn J-thread spec this time. It made pipe threads and Acme threads a breeze.

Its made and sold by member here... And I'm not affiliated, just a happy customer.

Sent from my Pixel 2 using Tapatalk

Bobw · Dec 8, 2018

pablo.casiano75 said:
Yeah but if you use the pitch dia. He will have no threads. He needs to measure the minor dia.. , everyone does things differently but just trying to help. I'm sure someone will know the exact drill size.

Sent from my Pixel 2 using Tapatalk

No. If you drill the minor diameter with a form tap, you will have a broken tap...

If you drill AT the pitch diameter, you will have full threads (in theory) with a form tap...

The material has to have a place to flow to.

If you drill at minor diameter with a CUT tap, you will have full threads.

If you drill at the PD for a CUT tap, you will have really really bad weak threads.

guest · Dec 8, 2018

Good formula for metric form taps: drill size = basic major dia - (% of thread*pitch)/147.06

So for 65% thread:

8-(65*1)/147.06 = 8-.442 = 7.558mm or .2975"

19/64 drill is .2968

djm77 · Dec 8, 2018

1111111111

Whysosharp · Dec 8, 2018

Just so your aware Guhring has a tap and drill chart for every imaginable class of fit. From cut taps to form and oversize threads a search for Guhring cut tap chart or form tap chart will get you what your looking for it’s a considerable amount of information.

Illinoyance · Dec 8, 2018

Link to the Guhring tap drill calculator:
Index - Guhring Inc - The Tool Company

rke[pler · Dec 8, 2018

pablo.casiano75 said:
Yeah but if you use the pitch dia. He will have no threads. He needs to measure the minor dia.. , everyone does things differently but just trying to help. I'm sure someone will know the exact drill size.

Perhaps you're thinking of the major diameter? Pitch diameter is between the minor and major diameter.

cobbadog · Dec 9, 2018

Just today I ahd to make a hole and thread it to suit M6 x 1.0 pitch. This required a 5mm drill bit so at best guess it should be a 7mm bit you need.

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What drill size for M8x1.0 6H form tap?

Finegrain

Diamond

pablo.casiano75

Aluminum

Newman109

Diamond

litlerob1

Diamond

DanielG

Stainless

Finegrain

Diamond

Bobw

Diamond

guest

Guest

pablo.casiano75

Aluminum

Bobw

Diamond

guest

Guest

djm77

Aluminum

Whysosharp

Cast Iron

Illinoyance

Stainless

rke[pler

Diamond

cobbadog

Plastic

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