Hi chaps - searched the forums but am unfamiliar with this topic so don't know where to go. I need to tap some Al heatsinks to mount output mosfets for an amp.
Can anyone suggest an online source where I can buy matching drill-bits, taps and compatible hext-bolts like i see in all the beautiful solid state builds in the forums ?
Metric sizes are preferable but as I'll want to buy them all in a set I don't mind inches either.
If anyone can point me to a source for sets and suggest appropriate sizes (in US terminology) for my application, I'd be very grateful. I believe mcmaster sells them but again, I dont know anything about the sizes.
Thanks again in advance! Cheers,
Can anyone suggest an online source where I can buy matching drill-bits, taps and compatible hext-bolts like i see in all the beautiful solid state builds in the forums ?
Metric sizes are preferable but as I'll want to buy them all in a set I don't mind inches either.
If anyone can point me to a source for sets and suggest appropriate sizes (in US terminology) for my application, I'd be very grateful. I believe mcmaster sells them but again, I dont know anything about the sizes.
Thanks again in advance! Cheers,
McMaster will have metric or imperial both, so take your choice.
Pick a screw size. Taps come in the same sizes 3mm screw, 3mm tap, #8 screw, #8 tap.
You need to drill a clearance hole, I forget the official term for it. The hole is large enough for the body of the screw, but leaves material where the threads will be. I don't have to do this, so I forget what number drill goes with what screw size, but McMaster ought to have that information in their catalog.
One alternative might be "self-tapping" screws. You drill the hole, but no need to tap it. The tip of the screw is beveled and will cut its own threads when first driven into a fresh hole. They work very well.
There are some amps using sheet metal screws into the aluminum as well.
And just drilling a full size hole for the screw and putting a nut on the end is not a bad solution.
Pick a screw size. Taps come in the same sizes 3mm screw, 3mm tap, #8 screw, #8 tap.
You need to drill a clearance hole, I forget the official term for it. The hole is large enough for the body of the screw, but leaves material where the threads will be. I don't have to do this, so I forget what number drill goes with what screw size, but McMaster ought to have that information in their catalog.
One alternative might be "self-tapping" screws. You drill the hole, but no need to tap it. The tip of the screw is beveled and will cut its own threads when first driven into a fresh hole. They work very well.
There are some amps using sheet metal screws into the aluminum as well.
And just drilling a full size hole for the screw and putting a nut on the end is not a bad solution.
The measurements on bolts are taken from the top of the thread...
You really dont need to tap the holes...
For m2,5 you would need 2mm drill or in ideal case 2,05mm one
m2 is pretty small,2,5 is ideal for fastening any type of device, such as chips and transistors.
Its mostly in use, ive never seen m2 being used in such case.
Try to find m2,5 8mm that have a little cut in them, add a bit oil and screw them in, there you go.
Ive found that m3 is sometimes too big, it can crack the device package.
If I was you, i would probably choose: ( search ebay
)
M2.5 X 0.45 pitch HSS 2H Tap & Tapping Size Drill Bit 2.05mm HSS
Socket Head Cap Screws M2.5 x 8mm
Im not sure how long will the chinese "HSS" hold but who knows...
You really dont need to tap the holes...
For m2,5 you would need 2mm drill or in ideal case 2,05mm one
m2 is pretty small,2,5 is ideal for fastening any type of device, such as chips and transistors.
Its mostly in use, ive never seen m2 being used in such case.
Try to find m2,5 8mm that have a little cut in them, add a bit oil and screw them in, there you go.
Ive found that m3 is sometimes too big, it can crack the device package.
If I was you, i would probably choose: ( search ebay
)M2.5 X 0.45 pitch HSS 2H Tap & Tapping Size Drill Bit 2.05mm HSS
Socket Head Cap Screws M2.5 x 8mm
Im not sure how long will the chinese "HSS" hold but who knows...
Last edited:
Wrong. If you drill a 3mm hole, the 3mm tap will fall into the hole.
There is no rule of thumb as the ratio changes as the bolts get bigger, but for am M3 tap you can use a 2.5mm drill.
You can buy a tap set which might have for example all three M3 taps (taper, second cut and blind) and the correct drill bit.
Staying with metric makes for very simple tapping and screwing into aluminium.
The relatively coarser thread of the M cf. the UNF (the more common bolt thread) gives good grip in aluminium. UNC is the coarse equivalent in imperial threads.
The thread angle in Metric it very simple to determine the pilot drill size.
Just subtract the pitch from the thread diameter for the pilot drill size.
eg M3 0.5pitch requires a 2.5mm drill.
M6 1mm pitch requires a 5mm drill.
Tapping into steel uses a very slightly bigger pilot drill. This reduces the thread engagement, but leaves sufficient to give the "strength" expected of the threaded steel fixing. I cannot recall a "rule" for tapping drill size into steel.
In the UNF & UNC sizes there are drill and tapping look up tables for the different materials.
Thread forming taps are very different from thread cutting taps. See the tap manufacturer's data.
The relatively coarser thread of the M cf. the UNF (the more common bolt thread) gives good grip in aluminium. UNC is the coarse equivalent in imperial threads.
The thread angle in Metric it very simple to determine the pilot drill size.
Just subtract the pitch from the thread diameter for the pilot drill size.
eg M3 0.5pitch requires a 2.5mm drill.
M6 1mm pitch requires a 5mm drill.
Tapping into steel uses a very slightly bigger pilot drill. This reduces the thread engagement, but leaves sufficient to give the "strength" expected of the threaded steel fixing. I cannot recall a "rule" for tapping drill size into steel.
In the UNF & UNC sizes there are drill and tapping look up tables for the different materials.
Thread forming taps are very different from thread cutting taps. See the tap manufacturer's data.
Thanks for the help so far.. As you might have guessed I can't recall having bought screws even once my stash comes from a few hours in front of the tv unscrewing bits from equipment headed for the trash heap. You can't imagine the number of screws and bits that come off a VCR or a mini photocopy machine.
It's just that they don't come with size labels
From what I've read so far that self tap screw thing sounds like a treat - but all the ones I have and the ones I can google are the very coarse type with very tapered threads and look almost like wood screws instead of the cylindrical metal type screws with hex heads.
Are there screws with the little slit or notch at the end like that ? Three step taps into a soft material is a bit too much of a fine touch for me..
my stash comes from a few hours in front of the tv unscrewing bits from equipment headed for the trash heap. You can't imagine the number of screws and bits that come off a VCR or a mini photocopy machine. It's just that they don't come with size labels
From what I've read so far that self tap screw thing sounds like a treat - but all the ones I have and the ones I can google are the very coarse type with very tapered threads and look almost like wood screws instead of the cylindrical metal type screws with hex heads.
Are there screws with the little slit or notch at the end like that ? Three step taps into a soft material is a bit too much of a fine touch for me..
I have always used 3mm bolts with a 2.5mm pilot hole for soft ali (heatsinks).
Manual 3mm tap, using a leisurely one full turn forwards and one half turn back, stopping to clear out swarf half way through.
I've never broken a tap yet (daft think to say ) and have been doing this for many years.
Steele is different and needs care and greater precision.
Manual 3mm tap, using a leisurely one full turn forwards and one half turn back, stopping to clear out swarf half way through.
I've never broken a tap yet (daft think to say
) and have been doing this for many years.Steele is different and needs care and greater precision.
Thanks for the help so far.. As you might have guessed I can't recall having bought screws even once
It's just that they don't come with size labels
From what I've read so far that self tap screw thing sounds like a treat - but all the ones I have and the ones I can google are the very coarse type with very tapered threads and look almost like wood screws instead of the cylindrical metal type screws with hex heads.
Are there screws with the little slit or notch at the end like that ? Three step taps into a soft material is a bit too much of a fine touch for me..
They sound like self tapping screws to me. Not good for mounting onto heatsinks.
When you tap, start working from the opposite side from your device (If available) - Why?
The exit of your tap will always be tighter than the start side.
So the first threads of the component side will be nice and tight rather than weak and slightly loose from trying to start the hole.
This is especialy important on thin metal thickness with those of little experience in tapping
Use cutting fluid also.
Regards
David
The exit of your tap will always be tighter than the start side.
So the first threads of the component side will be nice and tight rather than weak and slightly loose from trying to start the hole.
This is especialy important on thin metal thickness with those of little experience in tapping
Use cutting fluid also.
Regards
David
I have this set, for US threads
Tap and Drill set
I'm sure you can get a similar for metric threads.
Use oil when you tap, and don't force it. Turn the tap until it gets hard to turn, then back it out, and clean off all of the bits of metal, then do it again.
It takes some patience, but you'll get a threaded hole eventually.
Randy
Tap and Drill set
I'm sure you can get a similar for metric threads.
Use oil when you tap, and don't force it. Turn the tap until it gets hard to turn, then back it out, and clean off all of the bits of metal, then do it again.
It takes some patience, but you'll get a threaded hole eventually.
Randy
If the heat sink thickness is limited and you don't want to drill all the way through, get a bottoming tap (or grind the tip off a regular tap) as well. That will help cut threads closer to the bottom of the drilled hole.
Chucking the tap in a small drill press and turning it by hand can help to insure that the tap goes in perpendicularly.
Chucking the tap in a small drill press and turning it by hand can help to insure that the tap goes in perpendicularly.
Hi all ! Based on the advice received here I went out and bought these - M3 tap, handle and 2.5mm drill bit.
Worked like a charm ! It didnt take much more than maybe 2 minutes to drill and tap one hole. It seemed easier to just twist the tap in all the way instead of one turn in vs half turn out - not sure if I should bother with that ?
Anyway I'll figure it out. Just wish I had tried this earlier - it's much easier than I thought it would be - if you get the right bits together that is.
And for that I owe you a big thank you chaps!
Worked like a charm ! It didnt take much more than maybe 2 minutes to drill and tap one hole. It seemed easier to just twist the tap in all the way instead of one turn in vs half turn out - not sure if I should bother with that ?
Anyway I'll figure it out. Just wish I had tried this earlier - it's much easier than I thought it would be - if you get the right bits together that is.
And for that I owe you a big thank you chaps!
Attachments
Last edited:
"... not sure if I should bother with that ?"
That depends.
As long as there is little resistance when turning (often the case in shallow holes in aluminIum) there is no need.
In the general case, if resistance is felt, than play cautious and back out. Taps are extremely hard and brittle. They snap easily!
Working out how to remove the snapped-off buried part of a 3mm tap in your otherwise pristine work is a life-enhancing experience .....
That depends.
As long as there is little resistance when turning (often the case in shallow holes in aluminIum) there is no need.
In the general case, if resistance is felt, than play cautious and back out. Taps are extremely hard and brittle. They snap easily!
Working out how to remove the snapped-off buried part of a 3mm tap in your otherwise pristine work is a life-enhancing experience .....
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.