Looks good Sjoerd - I don't think you will have too many problems with your arrangement.
Bambadoo, thanks for your list of issues. I will try to translate it and see if there are any other issues I need to include in the update
The problem is not with Jim's boards - I need to get arond to updating the documentation to include all the issues that have been raised over the last few buils.
IIRC about 100 nx-Amplifier sets have been sold, probably half to 2/3 assembled. for sx-Amp it much less because its still quite new out there (boards only released last year.)
Bambadoo, thanks for your list of issues. I will try to translate it and see if there are any other issues I need to include in the update
The problem is not with Jim's boards - I need to get arond to updating the documentation to include all the issues that have been raised over the last few buils.
IIRC about 100 nx-Amplifier sets have been sold, probably half to 2/3 assembled. for sx-Amp it much less because its still quite new out there (boards only released last year.)
Very good points gaborbela. I broke off 2 taps when I build my Ovation 250 amp (2006) and had to re-position the board on the heatsink. The quarter turn forward, quarter turn backward rule cannot be stressed enough - and use decent lubricating oils as well - like WD40.
Here is a quick intro to tapping heatisnks from YouTube https://www.youtube.com/watch?v=LuqliWT1k5A
Thanks guys! I think it is going really well. Apart for this slight setback that is 🙂
I was going for the fast way with a machine tap in my power tool 🙂 I just use the slip to be sure not to break it. It broke when I reversed after the first few millimeters. It worked for about 60 holes in total.... and now it died. Oh well, a new machine tap costs about 6 euro's. This one was only 1 euro at a flea market ;-)
It's a ***** job to get the old tap piece out so I will go for a new hole just next to the transistor and use a clamp to secure it. It is one of the small ones so no problem there.
I was going for the fast way with a machine tap in my power tool 🙂 I just use the slip to be sure not to break it. It broke when I reversed after the first few millimeters. It worked for about 60 holes in total.... and now it died. Oh well, a new machine tap costs about 6 euro's. This one was only 1 euro at a flea market ;-)
It's a ***** job to get the old tap piece out so I will go for a new hole just next to the transistor and use a clamp to secure it. It is one of the small ones so no problem there.
Last edited:
SjoerdSmits,
And anyone else who doesn't have to deal with this where you can't just move over and tap another set of holes the normal method to remove a broken tap like that is to EDM burn out the tap with an electrode. Not something you do in your garage or shop. A couple points for those reading this who haven't done this before is to remember with aluminum to use a two flute tap, never use a tap meant for steel with four flutes you will break that for sure. The best method to do this carefully is if you have a small drill press. Hold the heatsink on the press table with a clamp, drill the hole through the plate and then without moving the plate retract the drill, remove it and replace that with the tap. Turn the chuck with your hand and use the proper lubricant, WD-40 is just so so as a lube for aluminum. There is specific taping oil for this from a company like Tapmatic or others. Turn the chuck by hand, back out every couple of turns and you will almost never break a tap. You don't realize that you are putting the tap in slightly off axis by hand without a holder, it is what is causing most of the tap breakage, the chips are a problem but being perfectly parallel to the hole is the real problem doing this by hand.
And anyone else who doesn't have to deal with this where you can't just move over and tap another set of holes the normal method to remove a broken tap like that is to EDM burn out the tap with an electrode. Not something you do in your garage or shop. A couple points for those reading this who haven't done this before is to remember with aluminum to use a two flute tap, never use a tap meant for steel with four flutes you will break that for sure. The best method to do this carefully is if you have a small drill press. Hold the heatsink on the press table with a clamp, drill the hole through the plate and then without moving the plate retract the drill, remove it and replace that with the tap. Turn the chuck with your hand and use the proper lubricant, WD-40 is just so so as a lube for aluminum. There is specific taping oil for this from a company like Tapmatic or others. Turn the chuck by hand, back out every couple of turns and you will almost never break a tap. You don't realize that you are putting the tap in slightly off axis by hand without a holder, it is what is causing most of the tap breakage, the chips are a problem but being perfectly parallel to the hole is the real problem doing this by hand.
Last edited:
Thanks for the tips!! I did use a steel tap and had to clear out aluminium with a screw driver after every hole tapped. So this is good info!
SjoerdSmits,
I hope you didn't misunderstand my English about the tap. The tap will still be made out of tooling steel but a tap made for tapping steel will have more flutes, typically four and these are not as deep as a two flute tap has. This gives more room for the chips in the tap and also changes the root diameter of the center of the tap different. There are chip cutting taps that are very aggressive but these are really for high speed production on a machine using a clutch driven tapping head.
I hope you didn't misunderstand my English about the tap. The tap will still be made out of tooling steel but a tap made for tapping steel will have more flutes, typically four and these are not as deep as a two flute tap has. This gives more room for the chips in the tap and also changes the root diameter of the center of the tap different. There are chip cutting taps that are very aggressive but these are really for high speed production on a machine using a clutch driven tapping head.
In the past I always used a normal steel tap now I'm using a steel blind tap .Those taps realy transport the aluminium outside the drill hole
Meanman,
We call those taps bottoming taps, they are meant to produce thread all the way to the bottom of a blind hole. They can be harder to start straight into the hole as they have no tapered lead section. They would typically be used after starting the tapping with a tapered tap and then followed by the bottoming tap in a blind hole.
We call those taps bottoming taps, they are meant to produce thread all the way to the bottom of a blind hole. They can be harder to start straight into the hole as they have no tapered lead section. They would typically be used after starting the tapping with a tapered tap and then followed by the bottoming tap in a blind hole.
You can begin with a tapared tap for a starting thread and end up with a bottoming tap.Last time a used it directly but drilled a 2,5 mm hole instead of a 2,3 mm hole without any problem.
Meanman,
Yes using a slightly larger hole will make things easier. The reality is since we aren't having to tighten to the maximum torque allowed by this size thread that shouldn't be a problem and is probably a smart thing to do to minimize the chance of breaking a tap. If you needed maximum holding pressure that would not be the thing to do.
Yes using a slightly larger hole will make things easier. The reality is since we aren't having to tighten to the maximum torque allowed by this size thread that shouldn't be a problem and is probably a smart thing to do to minimize the chance of breaking a tap. If you needed maximum holding pressure that would not be the thing to do.
I know but the funny thing is when you buy different brands of taps the one drill a 2,5mm hole an other brand says use a 2,3-2,4 drill.
Meanman,
If you would look in a machinist manual you would see there is a range of hole sizes for a particular tap thread size. This is based on the percentage depth of thread engagement and the intended holding pressure required. There is generally a drill size for a common thread engagement value that will give a minimum holding force and engage a specific depth of thread engagement. That would generally be 75% thread engagement. Here is a typical drill chart but there are others that show the different range of thread engagement.
Tap Drill Chart
If you would look in a machinist manual you would see there is a range of hole sizes for a particular tap thread size. This is based on the percentage depth of thread engagement and the intended holding pressure required. There is generally a drill size for a common thread engagement value that will give a minimum holding force and engage a specific depth of thread engagement. That would generally be 75% thread engagement. Here is a typical drill chart but there are others that show the different range of thread engagement.
Tap Drill Chart
The hole size is determined by the thread depth and the engagement required.
For aluminium near 100% engagement would be used, whereas for steel one could reduce down to 70% engagement.
For metric thread one simply subtracts the thread pitch from the thread diameter to arrive at the 100% engagement pilot hole diameter.
eg for a 6mm x 1mm pitch thread, one would drill a pilot hole @ 5mm for 100% engagement and 5.1mm for 90%, 5.2mm for 80% and 5.3mm for 70%
For aluminium near 100% engagement would be used, whereas for steel one could reduce down to 70% engagement.
For metric thread one simply subtracts the thread pitch from the thread diameter to arrive at the 100% engagement pilot hole diameter.
eg for a 6mm x 1mm pitch thread, one would drill a pilot hole @ 5mm for 100% engagement and 5.1mm for 90%, 5.2mm for 80% and 5.3mm for 70%
Usually you would try to keep aluminum thread fit tighter than steel, but not 100% engagement. That would be an interference fit. You wouldn't be able to install the screws in gummy material like heat sink. I haven't got my Engineer's Handbook handy, but if I recall correctly grade 8 thread fit is 80% engagement.
Another important issue with aluminum is you need a sharp drill bit. If you make the aluminum hot during drilling, it will go soft and have a much better chance of sticking to the tap. This is more of an issue in heat sink and low quality casting than is normal 6061 T6.
Another important issue with aluminum is you need a sharp drill bit. If you make the aluminum hot during drilling, it will go soft and have a much better chance of sticking to the tap. This is more of an issue in heat sink and low quality casting than is normal 6061 T6.
I've found that using Alumtap lubricant makes tapping easier. If doing through holes, I've also found that a spiral tap is much easier to use than a four flute tap.
the tolerances of the male thread and female thread ensure that @ 100% engagement there is no interfernce fit.
You can have a full female thread and a full male thread and they screw on to each other.
It sounds like your definition of 100% thread engagement is different than most. By the Engineering Handbook (industry standards) 100% would male and female threads both coming to a 60 degree point with no radius. This makes the male thread weaker due to the smaller ID and lack of radius allowing for easier fracture.
Tollarances are allowable over or undersize. Tollarances could easily cause press fit in this situation. I think the term you are looking for is clearance, which means less engagement.
Your suggested tap drill sizes are accurate. Threads are cut on a 60 degree angle. If you do the trig on the thread pitch, you'll see there is a lot of room between both threads. They are never as tight fitting as they seem.
Lets stick with the amps guys! Appreciate your insights, but I think this belongs in the Equipment and tools etc thread
🙂
🙂