thread tapping

[tiburon]

Hi,

I hope someone here can give me a crash course on thread tapping. I have to tap my Simworld knobs and I borrowed this utterly crappy tap and die set from a friend. I drilled a 3,2mm hole for a 4 mm tap and screwed the M4 x 7 (?) tap through. But, the M4 set screw didn't fit. It was too small and just fell through the hole.
So that was one knob (half) ruined and before I ruin any more of them I thought I'd ask if anybody knew what could have gone wrong.
Thanks in advance.

Martin

[fordgt40]

Either the tap is wrong or the grub screw is not 4mm. Test both the tap and grub screw with a 4mm nut and see which is correct.
Probably find that the grub screw is actually 3mm :)

David

[tiburon]

No, the grub screw is M4, the tap however doesn't fit in a M4 nut. Must be the crappy quality.
Is there anybody in the Netherlands who would be kind enough to help me tap those knobs ?
I can't afford a better quality set at the moment.

[riche543]

Sounds like wrong tap , metric or imperial or wrong pitch ( thread spacing ) is there a pitch gauge with the tap & die set. If so you check pitch on grub & pitch on tap.
Good luck.
Riche.

[tiburon]

Is it possible to screw up the tapping ? (pun intended) I mean, the hole I've made is wider at the beginning then at the bottom, where the grub screw almost fits. Sorry to keep asking but I don't want to mess up any more expensive knobs.

[fordgt40]

There are three stages of taps. Taper - used to easily start the tap, Middle and then End tap used for blind holes.
If the grub screw "fell through" the hole and the grub screw fits a 4mm nut then the tap must be wrong. Even if you "screwed up" when using the tap, it should not let the grub screw "fall through"

Just in case the knob material was so soft that the tap cut a hole rather than a thread, try it out on another material eg aluminium, making sure that you use some oil and reverse the tap to break the chips.

David

[tiburon]

Thanks David. The material is of course resin which is pretty soft. the tap set I have has 2 M4 taps that are marked M4x0,7 and 4x0,75. There's no taper and they have pointy ends so I guess this is the middle variety. I'll try your suggestion and make some holes in aluminium.

[Westozy]

All good advice guys cheers!

Here is a great metric thread tapping chart - http://www.engineersedge.com/manufacturing/metric-iso-tap-drill-chart.htm
It is important to use the right tapping drill. In your case 3.3mm or 1/8" is the right drill, it will do for both M4x0.7 and M4x0.75 in resin. This is the same thread I use in all of my Boeing and Airbus range of replica knobs!

Cheers Gwyn (Westozy)
Aerosim Solutions

[tiburon]

Thanks Gwyn.
Am I right in thinking that 4 x 0,7 is the most widely used for metric threads ?
I found a supplier who sells separate taps so I can order a good quality one.

[Westozy]

Thanks Gwyn.
Am I right in thinking that 4 x 0,7 is the most widely used for metric threads ?
I found a supplier who sells separate taps so I can order a good quality one.

I buy the knob grub screws in bags of 100 on Ebay, I have both taps in my set but can't remember which one it is, I'll have a look when I get home and get back to you on this!

Cheers Gwyn

[vidarf]

Place the screw in the grooves on the tap bit. They should be exactly the same width. Hold the threads against each other. Should be a perfect fit.
If not, you have the wrong bit. When tapping resin, I've found that if you use a small battery powered screwdriver, it's easier to start. If you use the tapping wrench, you might damage the start of the hole. And as always: one turn, a half turn back when you're making threads! For long holes, remove the tapping bit once or twice to remove debris.

PS: before you start using new and unfamiliar equipment, try it out on scrap material first! That lesson is self-taught. The very expensive way...

[tiburon]

Thanks, that's exactly the kind of advice I was looking for. I'm waiting for the high quality bit I ordered to replace the toy bits I borrowed from a friend. How can you time one turn with an electrical screwdriver ? Doesn't that turn way too fast ?

[vidarf]

It does not matter for the first 5mm - no need to go in reverse before the bit has gone in a couple of mm. :) Just take it slow. Use the lowest gear if applicable. As soon as the tapping bit has "gotten hold", i.e. started to screw itself into the material, switch to the tapping wrench.

Since a tapping bit is tapered on the end, the first 5mm does not create enough debris for any clogging to occur. By doing "one right, a half left", you break up the cutouts. For metal, you should use a half turn then a quarter turn back.

With some experience, you will end up putting the tapping bit in the drill/screwdriver and go to town with it. :twisted: But don't do that unless you know what you're doing. :)

I have a Bosch GSR 10,8-2-LI Professional, and it is one of the most versatile tool I own! A small screwdriver like that makes simbuilding a lot easier!