Tapping holes

N5GTi6

N5GTi6

Well-known member
VIP Paid Subscriber
1000+ Posts
Fellow Frogger
Joined
Mar 2, 2004
Messages
1,836
Location
Sydney
I have a need to enlarge a current M10 1.5pitch threaded hole to an M12 1.5pitch. It's in cast alloy and a through hole.

I have the M10.5 drill, but I've just found that I have 2 X M12 taps in 1.75pitch - not a 1.5pitch. So I need to buy a tap.

So, the question is - can I get by with just an intermediate tap ? or just a taper tap, or do I need to go through first with a taper tap and then an intermediate tap as well ? I'm thinking just an intermediate tap but since they're quite expensive - especially for a single use, I'd like to make sure I'm getting the right tool.

Cheers

Justin
 
You should be able to go through with just a taper tap.

Tap sets can be bought in sets of three, a taper, intermediate and a plug tap.

I bought a large metric tap and die set a few years back, cost about $300 but have not had to buy a tap since. Is definitely worth the investment for the convenience.
 
Agree with Col. As you can go right through, the taper tap will be good. It is the easier and better "starter" and thread cutter for a new thread, and the top half is full thread, so will cut full thread all the way if it can protrude through the material.
 
Why not just use the 1.75? In alloy I understand it’s a stronger thread than 1.5, depending on the depth.
Don’t have to buy a new tap.
 
Be careful as some size thread pitch bolts & studs are not readily/commonly available.
 
Clicktracy said:
Why not just use the 1.75? In alloy I understand it’s a stronger thread than 1.5, depending on the depth.
Don’t have to buy a new tap.
Click to expand...
Hi - I haven't done the calcs but I suspect the roots of the M10 1.5 thread would overlap the crests of the M12 1.75 thread, with incomplete thread form. I agree with the 1.75mm pitch being better for alloy though.
 
  • Like
Reactions: dvr
Yep - I'm buying the bolt from Lee Bros - they have plenty of stock of 12.9 bolts - probably get the tap from there as well. I'm replacing a known weak 10.9 M10 bolt with a 12.9 M12 bolt. I believe I'm tapping cast aluminum alloy of some sort - I don't know any further. I hadn't considered exactly how close in size these are.

Cheers

Justin
 
I'm making a number of brake caliper plates at the moment and have been buying taps off ebay as I need them. Quick delivery (few days from Wentworthville) cheapish (about $8 give or take) and good quality (hss). It's critical to use the correct size final drill and ensuring the tap doesn't "cock" but is square.
 
dvr said:
I'm making a number of brake caliper plates at the moment and have been buying taps off ebay as I need them. Quick delivery (few days from Wentworthville) cheapish (about $8 give or take) and good quality (hss). It's critical to use the correct size final drill and ensuring the tap doesn't "cock" but is square.
Click to expand...
That's cheap - I've paid $14 delivered.

I'm using a 10.5mm drill for an M12 X 1.5 bolt.

Another tip it to use cutting compound - learnt that years ago the hard way... ;)

Cheers

Justin
 
Andrew Watkins said:
Would a helicoil in the appropriate larger size be a way forward?

This gives a thread which is said to be stronger than original

Andrew
Click to expand...
It's actually the strength of the bolt I'm after - hence going from 10.9 to 12.9 and M10 to M12. This bolt is a single point of failure and anecdotal evidence suggests that the bigger bolt is up for the job.

Cheers

Justin
 
N5GTi6 said:
That's cheap - I've paid $14 delivered.

I'm using a 10.5mm drill for an M12 X 1.5 bolt.

Another tip it to use cutting compound - learnt that years ago the hard way... ;)

Cheers

Justin
Click to expand...
I use this.
1632977373446.png
 
N5GTi6 said:
It's actually the strength of the bolt I'm after - hence going from 10.9 to 12.9 and M10 to M12. This bolt is a single point of failure and anecdotal evidence suggests that the bigger bolt is up for the job.

Cheers

Justin
Click to expand...
Going from grade 10.9 to 12.9 may or may not be the way to go depending on what type of force/s you are trying to protect against.

I fabricated a transfer shaft to replace the original transmission in a 1920s motorcycle. The bolts securing the sprockets to the hubs also take all of the torsional load. When I went to purchase 12.9 bolts my bolt supplier questioned the application and when I told him he said the 12.9s would most likely fail before the 10.9s when subject to that type of force.
I purchased the 10.9s and haven't had an issue as yet. I might add there are only two 6mm bolts securing each sprocket and they are transferring 10 HP.
 
Taping castings is always taking a gamble on the quality/material of the casting. Helicoil might be one solution, another would be to insert a grubscrew and loctite that in place for good and use a nut if things allow. Whenever possible, that is what I do.

Might want to check again, I seem to remember you need a 10.8mm hole for a M12 thread. Not that you won't be able to thread but your thread might end all chewed up.
 
schlitzaugen said:
Taping castings is always taking a gamble on the quality/material of the casting. Helicoil might be one solution, another would be to insert a grubscrew and loctite that in place for good and use a nut if things allow. Whenever possible, that is what I do.

Might want to check again, I seem to remember you need a 10.8mm hole for a M12 thread. Not that you won't be able to thread but your thread might end all chewed up.
Click to expand...
M12 metric fine is a 10.8mm drill, M12 metric coarse is a 10.2 mm drill.
 
Oh and of course M12 intermediate (1.5 pitch) is a 10.5mm drill.

I'm still wondering what type the forces are that induce failure in the original 10mm bolt?
Regardless of the tensile strength of the bolt clearly the cast alloy thread is never going sustain the maximum torque (to the point of failure) capability of even a 10.9 bolt unless it is an extremely deep thread?
For example the maximum torque value of a M12 12.9 bolt into alloy is almost identical to the max torque value of a M10 10.9 bolt into cast iron.
Bigger/tougher isn't always the answer.🤷‍♂️
 
PeterT said:
You'll need to expand and explain your statement here. Are you saying the maximum torque of the bolt material is the same? Or are you saying the shear stress of the threads in the parent material being torn off is the limiting factor?

Also, the best cutting fluid for aluminium is kerosene, WD-40 etc. I wouldn't waste Trefolex on it.
Click to expand...
The torque value is based on the deformation limits of the threaded parent material. This is normally calculated on the minimum thread engagement being 3 times the bolt's diameter. This is engagement around the thread, roughly Pi, so a 10mm bolt should be screwed down a minimum of its own diameter (10mm) to theoretically torque safely to the recommended limits of the parent metal.
A 12.9 bolt has a significantly higher torque value than a 10.9, but unless it's being used with an equivalent grade nut it is highly unlikely you could make use of the torque difference. Certainly on the face of it, screwing a 12.9 bolt into cast alloy seems a bit of a waste.
Again it's hard to comment on whether a 12.9 would offer any advantage over a 10.9 in this instance without knowing what forces it is resisting. Indeed under some circumstances a 12.9 may not survive as well as 10.9 as it is more brittle. The fatigue endurance strength of a 12.9 bolt is identical to a 10.9.
 
driven said:
You need a Bolt strength calculator
Still gets down to the clamping force generated
Click to expand...
Trouble is we still don't know what this bolt is doing. For all we know it could be a lock nutted pivot point for a tensioner arm?? In which case it's clamping force would have little revelance to it's performance in this role.
If clamping force was the only criteria one would use a 1.25mm pitch not a 1.5mm anyway.
 
You must log in or register to reply here.
Top