Tapping/threading a drillhole (prolly offtopic)

[p1ckf1sh]

I am just trying to fabricate something lockpickish, and I need a grubscrew to secure something to something else...

Now, my grub is M4 (3.2mm) and I have thread cutting bit in according size. My question is, what hole should I drill? Should I use a straight 3mm or a M4 (3.2mm) drill bit? The way I understand threading is that you have to keep the drilled hole a slight bit smaller to keep room for the thread. Is this compensated for when you use M4 sized parts exclusively?

[Octillion]

Just do a Google search for a chart. Here are the first few results I got:

http://www.engineersedge.com/tap_drill_chart.htm
http://www.iroquois.free-online.co.uk/drilltap.htm
http://www.efunda.com/designstandards/screws/tapdrill.cfm

[Shrub]

The correct tapping drill for a M4 is 3.3mm but i use 3.2mm and a 3mm will be ok on anything but the hardest of materials.

Other stuff you may want to use to make sure is,

Core 3.1412mm
Depth 0.4294mm
Pitch 0.70mm
Effective dia 3.545mm
Clearance drill 4.10mm

Hope that helps.

[Shrub]

I hate it when i get beaten to posts because it takes me too long to type lol

[Octillion]

Sorry... But at least you tried harder in writing up yours, I just slapped some links together.

[p1ckf1sh]

Whoever was first - who cares. You both gave a knowledable and helpful answer in a very short time. I did some threading training on scrap metal and it works out pretty well even though I bought the cheapest thread cutter I could get.

As always, great answers, thanks again to you guys!

[Shrub]

No worries and i was only joking lol

The cutter for a hole is called a tap and the tool for putting a thread on a shaft is called a die

[Octillion]

No worries and i was only joking lol

Yeah, I gathered that much

[HeadHunterCEO]

I don't think asking how to properly tap a hole is an off base question.
using a center punch will ensure you are starting exactly where you want to drill.
don't push with excessive force becase this can cause the drill point to walk off while it travels through the material resulting in a mis drilled hole even if you used the center punch.

back the tap off constantly and clean it while tapping deep hole in excesivly hard or soft materials.

[Shrub]

Also if in hard materials use all 3 taps, you start with the taper then the second then the plug to finish off.

Personally i dont like the point they seem to put on the plug taps nowadays so i grind the plug flat at the end so it does a blind hole.

As said its not off tangent at all i think we need more people asking questions like this.

[bembel]

Also use some oil when cutting the thread.

Also if in hard materials use all 3 taps

I used this 3 taps system as an apprentice about 20 years ago. Can't tell you how many I broke when I used them with a manual cutter.
Nowadays I use single taps and a power drill. Sounds dangerous, but so far I never broke one of them again, even in hardest steel. Just don't forget the oil.

[devildog]

Hey! Bembel's back! Welcome back, stick around this time ; I remember you from those VERY nice homemade picks you constructed a while back; anyone who wants to see a beautiful example of DIY picks should dig up Bembel's old post, I think it's in the 'show off your homemade picks' thread, and have a look at his work.

[bembel]

Wow, thanks.
But I really wasn't too far away.

P.S. Now that you mention it: I was wondering if Romstar is still around?

[devildog]

Long story, that I'm not completely clear on, but not really. Due to illness, if I remember correctly.

[p1ckf1sh]

Shrub, I am not using a system of three taps but rather a single bit, which works fine in hard 1mm spring steel and 10mm fastener screw steel. As I said, I got the cheapest set, which got me 6 bits in different at 10 eurobucks.

Bembel, using a powerdrill with those single bit taps really works? I should give it a try, sounds good. Do you use really low rpm for that?