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Tiger
13th Dec 2005, 11:04 AM
Dear all,

Have 2 questions for you to consider.

1. I have scrounged together some taps and dies mainly Whitworth (BSW)and metric. I have been told that UNC and UNF are probably the most commonly used threads and that I should get some. Question is there are so many thread types out there, which ones are the essentials as we can't hope to get them all.

2. Does anyone know what tolerances are allowed when tapping, eg say a 5.1 mm drill bit is specified for a 1/4'' BSW tap and you don't have a 5.1 mm drill, can you get away with a 5 mm drill or 5.5 mm drill bit. Is there a formula that you can use to quickly work out what is allowed.

Thank you in advance for any replies.

savage
13th Dec 2005, 11:31 AM
Dear all,

Have 2 questions for you to consider.

1. I have scrounged together some taps and dies mainly Whitworth (BSW)and metric. I have been told that UNC and UNF are probably the most commonly used threads and that I should get some. Question is there are so many thread types out there, which ones are the essentials as we can't hope to get them all.

2. Does anyone know what tolerances are allowed when tapping, eg say a 5.1 mm drill bit is specified for a 1/4'' BSW tap and you don't have a 5.1 mm drill, can you get away with a 5 mm drill or 5.5 mm drill bit. Is there a formula that you can use to quickly work out what is allowed.

Thank you in advance for any replies.
Hey Tiger,
I you aren't in a hurry, I can go through some papers tonight and scan them, they are tables with tap sizes, drill size and alternate drill size if the correct one is unavailable. they are a bit old and tatty but always get me out'a trouble, they cover all thread type and size. P.M. me if interested and I'll put'em up here so all can getthem if needed.

JDarvall
13th Dec 2005, 11:53 AM
Dear all,

Have 2 questions for you to consider.

1. I have scrounged together some taps and dies mainly Whitworth (BSW)and metric. I have been told that UNC and UNF are probably the most commonly used threads and that I should get some. Question is there are so many thread types out there, which ones are the essentials as we can't hope to get them all.

2. Does anyone know what tolerances are allowed when tapping, eg say a 5.1 mm drill bit is specified for a 1/4'' BSW tap and you don't have a 5.1 mm drill, can you get away with a 5 mm drill or 5.5 mm drill bit. Is there a formula that you can use to quickly work out what is allowed.

Thank you in advance for any replies.

Hey mate,

The threads you can buy from local hardware stores are usually the common ones. Coarse usually. And there fine. Unless your building the space shuttle. You know what I mean. What I do, is just go in check out the bolts, pick one I think is the right diameter and length for what I'm doing and just go to the drill bit section, pick up the corrisponding tap, like say 1/4" and just line up the thread of my bolt to the tap( I just tear the tap out of the plastic coating a bit). If they interlink you've got a match. No doubt they will. But worth a check.

As for the tapping hole. You don't have to have to use the drill bit they specify on the taps packaging. Actually, I prefer a larger bit. Cause that means less effort and wear to your tap when cutting the thread. And the strength is still adequate even though the full thread of your bolts not engaged. IMO. ....so, like you said sounds fine. 5.1mm they recommend. 1/4" = 6.35mm. That means your cutting a thread .625mm around the hole. If you drilled 5.5 instead. Means only .425mm of thread is cut. Plenty of grip IMO (did I get the maths right ?)

I'd definetly get some special drilling lube though. By it from nut and bolt stores. What the pro's use. It really speeds things up and definetly extends the life of your tap. Expensive , but it will last a while cause you only need a drop per hole.

:)

Barry_White
13th Dec 2005, 02:09 PM
Dear all,

Have 2 questions for you to consider.

1. I have scrounged together some taps and dies mainly Whitworth (BSW)and metric. I have been told that UNC and UNF are probably the most commonly used threads and that I should get some. Question is there are so many thread types out there, which ones are the essentials as we can't hope to get them all.

2. Does anyone know what tolerances are allowed when tapping, eg say a 5.1 mm drill bit is specified for a 1/4'' BSW tap and you don't have a 5.1 mm drill, can you get away with a 5 mm drill or 5.5 mm drill bit. Is there a formula that you can use to quickly work out what is allowed.

Thank you in advance for any replies.

Tiger

I think you will find that UNC is the same as Whitworth. What they have done is change the outside of the nut and the head of the bolt to fit metric spanners.

With imperial threads there is an equivelant imperial drill to suit the tapping hole and for 1/4" tap I use a 3/16" drill and if I don't know the correct size drill I just hold the drill bit closest to the Tap size and hold it against the tap and just make sure the drill bit will drill a hole equal to the dia of the bottom of the thread.

Or have a look here. Google is your friend.

http://www3.telus.net/public/aschoepp/tapdrill.html

Termite
13th Dec 2005, 02:14 PM
Tiger

I think you will find that UNC is the same as Whitworth.

From memory, only up to 1/2" then they differ.

aussiecolector
13th Dec 2005, 03:21 PM
From memory, only up to 1/2" then they differ.

Actually their all different. The tpi's are the same except 1/2" and may be some of the bigger ones but the thread angle on withworth is 55 deg rather than the 60 deg on every thing else. You can get away with interchanging them but it's not right.

Andy Mac
13th Dec 2005, 03:35 PM
One trick I learnt (from a Kiwi fitter) for metric tapping holes, is to subtract the pitch from the diameter of the bolt. So M6 at 1.25 pitch gives 4.75mm tapping drill.
It seems to work OK, don't know about being technically correct, but then all my drill bits are in Imperial, so I pull out the drill conversion chart or use the verniers anyway....might well have consulted the chart to begin with!!:o

Cheers,

Greg Q
13th Dec 2005, 03:50 PM
Yes, I use that rule of thumb too. I think the ISO people (or DIN, whoever)
made the standard so the thread root was the same as the pitch, hence the
rule.

Edd
13th Dec 2005, 04:19 PM
UNC, UNF and Metric threads all have an angle of 60°, which makes sense as a triangular file's corners are this angle, which is good for repairing them.
Whitworth (and other British threads) have an angle of 55°, don't bother with these, just buy an odd one if you have to match a thread.
ACME Thread form of 14.5° (I think), good for strength. I don't think they make taps and dies for this.
BA have an angle of 47.5°. I think they only make taps to fit certain screws, only buy if you need them for a job.

If you are buying a set, get metric with 2 or 3 taps/size. Start with a coarse set if it's either coarse or fine. If you need other taps and dies, buy as you need them.
Here's the other neat thing that works for regular metric threads (coarse at least):
D=T-P
Where D is drilling size, T is tap diameter and P is the tap's pitch. Technically it should be the same as the minor diameter of the tap, which is the drill size that a chart tells you. Just read the (a) chart.
You probably know about starting, tapered and plug (or bottoming) taps. A set of metric taps from Hare and Forbes might be a start. My father has a Japanese set from a store called gasweld. 110 pieces for ~$300, which has various fine and coarse metric threads with starting and bottoming taps and what not, which will last a lifetime :)

Ashore
13th Dec 2005, 05:37 PM
Dear all,

Have 2 questions for you to consider.

1. I have scrounged together some taps and dies mainly Whitworth (BSW)and metric. I have been told that UNC and UNF are probably the most commonly used threads and that I should get some. Question is there are so many thread types out there, which ones are the essentials as we can't hope to get them all.

2. Does anyone know what tolerances are allowed when tapping, eg say a 5.1 mm drill bit is specified for a 1/4'' BSW tap and you don't have a 5.1 mm drill, can you get away with a 5 mm drill or 5.5 mm drill bit. Is there a formula that you can use to quickly work out what is allowed.

Thank you in advance for any replies.

1 The essential ones are the ones you need for a job
This will depend on what your working on , where it was built etc
I would say Metric are proberly the most common today

2 For tollerances I have included some charts for tapping drill sizes, clearance sizes etc but they dont have alternate drill sizes that savage is going to post, and I think that is what you need.


The charts below are from P&N for commercial thread production
giving tapping drill sizes and TPI and they do show that all the threads are DIFFRENT
and this is only for Diameter and threads per inch , it doesn't even mention thread angles, so people please stop posting replys telling people that this thread or that is the same as another thread , because they arn't

http://www.woodworkforums.ubeaut.com.au/attachment.php?attachmentid=16482&stc=1&d=1134455594

http://www.woodworkforums.ubeaut.com.au/attachment.php?attachmentid=16483&stc=1&d=1134455594

http://www.woodworkforums.ubeaut.com.au/attachment.php?attachmentid=16484&stc=1&d=1134455594


http://www.woodworkforums.ubeaut.com.au/attachment.php?attachmentid=16485&stc=1&d=1134455594


Rgds


Ashore

JDarvall
13th Dec 2005, 06:47 PM
I reakon, if you really want to get into it....

Just get one of those thread pitch guages, that you line up to a thread to learn its tpi in Whitworth. You'll get by fine with that. Get them from the bolt and nut suppliers. While your their get a little chart from the nut and bolt suppliers. It will be up to date with everything standard.

Means you can use any old bolt thats lying around your shed. Just identify it with the guage, or take the bolt in and say 'can I have a tap that fits this bolt, I think its a ....... . He'll sort it out....

MICKYG
13th Dec 2005, 08:43 PM
Tiger, there are a lot of Metal Rulers which have quite a bit of information stamped into them on the rear. The information is very useful with the metric & and imperial conversions. It has tap and also hole size to drill for a particular thread. You will find these rules at most good hardware stores. I will post a picture of one of mine tommorow night which will give you an idea or two.

Regards Mike.;)

Schtoo
14th Dec 2005, 02:10 AM
UNC and UNF are not useful, till you need them. For example, I have a 1/2" UNF die, but no tap to suit. That's fine, because it matches the thread on larger drill chucks. Didn't get the 3/8" UNF though did I? Anyways, metric and Whitworth are more than enough. But everyone has already told you that.

On the drilling, lots of variables in there.

Take the last tapped things I did. 6mm thick mild steel, with 5mm allen head cap screws to go into it. They have to be seriously reefed down, and also put up with some abuse. The correct drill for a standard 5mm tap is 4.2mm, which is what I drilled at. I want as much strength as I can get out of the threads.

Previous ones were 6mm bolts, 20mm of thread engagement, also maximum strength out of the whole shebang, and again, maximum thread depth.

A few months earlier, I needed to fasten down a piece of MDF to a 3mm thick steel frame. Decided to (foolishly in hindsight) to use 5mm screws, about 30 of them. The MDF was only a top, nothing structural. I also wanted to get it out of the way ASAP, so I drilled them at 4.5mm and then ran the tap in with a battery drill. Quick, plenty strong for that and all was good. I shoulda used self drilling screws though...


I don't know how much sense that makes to you, or even to me. But the bottom line is that if you aren't going to give the threads a hard time, or if the tap is going into steel, then a slightly larger drill bit isn't going to hurt anything. If you are going to give the threads some trouble and/or the tap is going into something soft, like aluminium, then erring on the small side might be better to ensure full depth threads.

Myself, if I am going to the trouble and expense of buying a tap, then I'll spend a little extra and buy the right sized drill bit to go with it, and look after the set.

Also, buy good stuff. The cheapo sets are garbage, and an awful lot of the 'better' sets aren't. Stick with HSS and you shouldn't get too many problems.


(I say the above, needing to replace my 5mm and 6mm tap/drill sets, as they are almost worn out. After just over a year...)

Edd
14th Dec 2005, 06:54 AM
Yeah one other thing, there are three types:
•Alloy
•HSS
•Tungsten Carbide Alloy
in order from weakest to strongest. If you buy a sutton one separately, it will probably be tungsten. Don't get steel alloy, at least go for HSS.

MICKYG
14th Dec 2005, 05:03 PM
Tiger

Here is a picture of the table mentioned last night.

Regards Mike.

Tiger
14th Dec 2005, 06:03 PM
Thanks, boys. You've given me the information that I needed. Particularly grateful to the guys who scanned stuff through (Ashore, MickyG) and Edd for his comments. I wasn't aware of the material composition of taps but I'll look out for the HSS ones. I assume that P & N and Sutton would be HSS as I've seen a few of their taps at flea markets.

Schtoo
14th Dec 2005, 06:34 PM
If yer looking at the flea markets, you might get lucky and find either cobalt HSS or possibly tungsten. Cobalt is better than HSS in that's it just more of everything, including the price. Tungsten is good if you are tapping nasty stuff like stainless or titanium regularly, problem is that it's brittle. That means where a HSS tap will let you know it's not happy, the tungsten will snap in the hole, and you are not going to get it out in any kind of hurry, if ever.

Don't restrict yourself to Suttons and P&N though, plenty of good stuff under other brand names, I just can't recall what they are right now. :D Generally, if it's nice and crisp and looks good, it will be a quality tool.

Going price last time I was at Wantirna was $1-3 per tap, all never used. Might also want to check out Pete's bargain centre in Croydon (?). He usually has a lot of that kinda stuff, some junk but some good and all very cheap.

And don't buy a used tap. Old never used ones are cheap enough you shouldn't have to buy a used one, unless it's a monster.


(BTW, if you see any endmills, I'll buy them off you!!! Might be a while before I can get there to pick them up though... :( )

Ivan in Oz
14th Dec 2005, 07:03 PM
May ask what might seem a "SILLY" question?
What are you Tapping:confused: :confused:

Some time back I TAPPED some well seasoned Hardwood.
It worked very well. Mind you, it was quite a coarse thread.
On a par to Coach Screws.

Edd
14th Dec 2005, 07:13 PM
Some time back I TAPPED some well seasoned Hardwood.
Haha. I tapped some softwood once for testing. Terrible thread. It needs to be drilled undersize because of the fact it's much softer than metal and the drill will easily make a bigger hole if not clamped securely. When I did it, the tap practically fell right through :o
Some cheap taps and dies can be OK for aluminium and maybe brass, though it's still not a pleasurable experience.

JDarvall
14th Dec 2005, 08:35 PM
And don't buy a used tap. Old never used ones are cheap enough you shouldn't have to buy a used one, unless it's a monster.


Just what I was going to say. Thats one old tool I'd never buy from a flea market. Unless maybe your tapping wood.

Buy new, I reakon,,,, heaven forbid you break one off in a hole.

Schtoo
15th Dec 2005, 01:22 AM
Last tap I broke was in the main ways for my lathe. Made a funny noise, then snapped off, leaving a little ugly bit sticking out, but not enough to get a hold of.

Ended up having to bash it through with a punch, then tapping the next size up. Luckily, I got a nice plug tap in the bargain. :D

I have tapped so many threads lately, I don't even check to see if it's square and true any more.

Oh well, with any luck by Sunday the thing will be running well enough for it to do it's first job. That will make me very pleased as I have wanted a lathe for over 10 years now, and I am so close now I can taste it.

Prolly a bigger high than my first casting. ;)

JDarvall
15th Dec 2005, 03:51 AM
If you find time, Schoo ....love to see a picture, ya smartypants. :)

Schtoo
15th Dec 2005, 04:20 AM
I took some, but left the camera at the workshop.

And the workshop is a 30 minute drive away...


The fun part is working out the order of making spindles, tailcentres, tapers and whatnot. Think I have it worked out now, but I am sure I'll blow it.

Just hope I get my 'steel' tomorrow morning. :D

Termite
15th Dec 2005, 06:26 AM
Haha. I tapped some softwood once for testing. Terrible thread. It needs to be drilled undersize because of the fact it's much softer than metal and the drill will easily make a bigger hole if not clamped securely. When I did it, the tap practically fell right through :o
Some cheap taps and dies can be OK for aluminium and maybe brass, though it's still not a pleasurable experience.

Regularly tap MDF for jigs.....no probs.
For tapping aluminium use kero as a lubricant...or WD40.

scooter
15th Dec 2005, 10:52 PM
Old taps are pretty hard, aren't they? The smooth shaft could make a good rod for a scraper burnishing tool methinks ;)


Cheers...............Sean

Schtoo
15th Dec 2005, 10:58 PM
Uhh, yeah they would.

So would old drill bits... ;)


Or, you could do what I did, and just buy some HSS rod, which arrived with the steel I got today. About $3 for a 6" length, but supremely useful stuff to have around...

I usually use a pin punch for scrapers myself. :D

scooter
16th Dec 2005, 12:36 AM
Gday Schtoo, thought the tap might be harder than drill bits.

Prob either will do anyway, both sufficiently hard I guess by the sounds.


Cheers................Sean, tapped out :)

Schtoo
16th Dec 2005, 12:56 AM
Well, come to think of it neither are as hard as they could be.

Yer prolly right, the taps are harder as they can and do snap, but you have half the body missing where it cuts, then a bunch of stress risers in there too, plus they are often hand held, etc, etc, etc. They have lots working against their longevity so I would think they back the temper off much more than might give an optimal edge.
The drill bit gets lots of stress because half it's bulk is missing, and it also under power and often bends in the hole. They be a lot softer than they could be to put up with that.

Next burnisher I'm going to use up a certain drill bit if it gives me any more trouble, particularly if I can't sharpen it well enough...

Solid tungsten.

Prolly be the most expensive burnisher on the planet. :D