Taps and Dies...shouldn't they match?

[zeeprogrammer]

Hi,

I'm trying to (not improve) but learn some basic skills. So I thought I'd have a go at making the machinist clamp in 'The Home Machinist's Handbook'.

Not my first attempt at cutting metal...I've made two machinist jacks and the brass mallet (with my own alum handle) from the book....and have made 'good' progress on a Model 2A osc engine...ah...but that's about it.

Anyway...back to the clamp...1/4-20 thread using a die on the screws and 1/4-20 tap on the clamps. Both die and tap from same (cheap) kit. The screw binds pretty badly. I've re-tapped and re-threaded, but as expected, little difference. I'm down to sanding the screws and have made good progress. Some binding left and I think I can get that out before the threads are gone.

I don't think the screws are bad. I tried a couple of 1/4-20 nuts...one goes on slick as a whistle while the other tends to bind a little.

Your thoughts would be appreciated...maybe it's just a cheap tap and die kit? The tap handle is certainly for crap.

Material is free machining steel.

And by the way...just how slick is a whistle?

Thanks.

 

[Maryak]

Zp,

Sounds like it might be your cheap set of taps/dies.

Quick and dirty way to remove the binding and get a nice smooth fit is to run the screws up and down the clamp with Brasso or any metal polish on the threads of the screws, works a treat as it removes high spots from both and gives a neat fit.

Hope this helps. ??? ???

Best Regards
Bob

 

[bearcar1]

Z', what you are encountering is most likely a case of "you get what you paid for". The less expensive tap and die sets can be problematic at best sometimes. For a someone that merely requires a threaded hole in something they are satisfactory, but for a nice clean and free thread a set of better quality will be the order of the day. Of course that will no doubt mean more $$$ for what you are getting. The taps may be dull and have not cut a clean, accurate thread and is causing the part being screwed into it to bind or has not cut a full depth thread and bottoming out of the mating piece is the result. If you can source a single 1/4-20 tap at the local hardware store and run it into your piece to clean out what has already taken place, you should come away with nicely fitting parts. The usage of oil while tapping and backing the tap or die out or off of the piece in order to clear the chips is a must, lest you come away with a torn, damaged or malformed threads. Good luck with your projects.

BC1

 

[zeeprogrammer]

Thanks all for the confirmation.

I'm okay with getting a cheap set for learning...and they work well enough for the odd job...but now I can invest in a better set knowing:

1) I really enjoy doing this, and
2) I can actually do this
and 3)...there's several people like you all out there willing to teach.

Thanks for the idea of using polish or brasso and run the screw in/out...I was sanding but it bothered me that I could only get the outer thread and not the inner. I'm thinking thought that brasso is a little fine...any suggestion on using something a bit more abrasive but liquid? Yeah...the binding is that bad. Although...not that the parts have cooled a bit...they work better...all I have to do is move north....

Again thanks.

 

[Maryak]

Zp,

OK how about the heaviest cutting grade of car polish, or even stronger, fine valve grinding paste mixed with light oil.

Best Regards
Bob

 

[zeeprogrammer]

Thanks. I'll check it out.
BTW...I've been enjoying the home show.

 

[scoop]

can you try to pinch the die a little in the holder to get it to close up a bit.it only needs a slight bit of tightening one side of the split of the die to work.just run the die down the part again to shave off the high spots.Go easy on the screws as you can break the die if you use too much force to close it,but you should only need a small ammount of pressure to do it.Of course if its a die nut you have then I am talking rubbish.

good luck Steve C

 

[tmuir]

Are the dies the spilt type?
If so do it up a little tighter in the holder so the gap closes a bit on the split and run it over your thread.
You will skim a tiny bit of the tap and that may be enough to fix your problem.
I bought a cheap set of BA taps and dies but for the main threads I cut I went and bought the taps and dies individually in HSS of a known quality brand and you can see the diference when you use the good ones compared to the cheap ones.

 

[tel]

And by the way...just how slick is a whistle?

Thanks.

'bout as slick as greased eel snot!

 

[SignalFailure]

Could it be that the rod used for the screw was a tad oversize or the hole undersize? In either case metal can get squeezed rather than properly cut and the resulting thread isn't good. If you could find another hole or screw with the same thread you migh be able to isolate the problem. Keep at it!

 

[Shaynut]

No one has mentioones using a slightly bigger drill bit and cut down on the % of thread, not much tho. :big:
Roland

 

[Shaynut]

Im bad that should be a d (mentioned

 

[Tin Falcon]

ZP:
A) Like you and many here when getting started I went out and purchased a set of tap and dies for threading. A basic set from sears /craftman . There are a coupe of problems with such a set.
1) These are really maintenance tools for chasing a thread or tapping an occasional hole.
2) the recommended tap drill size stamped on the tap is limited to 64ths there is no allowance for material or % of thread engagement.
3) Sets do not contain the sizes needed for model engineering.
Hand taps should really be in sets of three for each size. Plug, taper, and bottoming.
4) most if not all of the basic machining books only show hand 4 flute taps like the ones show in sets. There are many great power or gun taps available for use but are not generally available in sets.
Hand taps require chip breaking

B) real tapping 101. what is not taught in the newby books
1) Power taps have less flutes are harder to break and need no chip breaking. they can be run under power.
2) Spiral point taps are best for through holes push the chip ahead.
3)Spriral flute taps are for blind holes and push the chips up and out.
4)Forming taps require larger tap drill sizes and form malleable material and do not make a chip. these can be used for blind or through holes.
These should be run fast under power.
5) Americas favorite power tool the cordless electric drill driver with clutch makes a great tap handle for power tapping.
My advice buy the taps you need for each project at hand soon you will have a nice collection.
Tin Falcon

 

[tmuir]

No one has mentioones using a slightly bigger drill bit and cut down on the % of thread, not much tho. :big:
Roland

True.

I usually drill to give 65% engagement which is enough for what I do.

Book 12 in the 'Workshop Practice Series' Drills, Taps and Dies by Tubal Cain is well worth getting and better still its pretty cheap. For someone new into model engineering its a great book explaining all the different types of drills and gives great tapping charts too.

 

[kvom]

The machinist clamps were the first project I ever made in the shop. I cut the threads on the lathe rather than using a die. This is a good thread for learning single-point threading. You can use the hole in the jaws to test the fit and cut deeper until it fits properly.

 

[zeeprogrammer]

Thank you all. Very helpful.
(Even the definition of slick.)

I was talking to a fellow at work...he's from Switzerland and had had a little machining experience way back when he lived there. He said, to thread a hole took 3 taps...a coarse, medium, and fine. He said that reduced the chances of breaking a tap since each go didn't take as much metal or use as much force. In fact, he said he was in the process of finding a set for his own lathe (I think I may have re-sparked his interest. He comes over to my desk almost every morning now to see what I've done.) I haven't seen any mention anywhere of such taps so far. Maybe a European thing or just Swiss. (Could even be communication between he and I.) I thought it might be handy for the small sizes model engineering tends to use.

Carl

 

[sparky961]

Although this isn't the solution for the tap/die issue, the comment on using "Brasso" or another metal polish reminded me of the trick I learned a while back for a few cheap and readily-accessible "lapping" compounds...

My favorite is toothpaste. Different kinds have different abrasives, but most are very mildly abrasive.

To polish copper to a beautiful finish (I used this for printed circuit boards), use a scouring cleaner such as "Comet". These usually contain some form of bleach, so be careful what you use it on/with. Cream kitchen cleaners also seem to do the trick, like "Vim" and similar products.

Pretty much anything that has a bit of extremely fine grit in it works nicely.

-Sparky

 

[Bluechip]

Carl

The taps referred to may be what I was informed were called 'Progressive'.

They all have about the same taper on the end, but are different O.D.'s

The 'First' looks a bit like a trapezoidal thread, the 'Second' less so, and the 'Third' cuts the full thread depth.

Obviously all three taps must be used to obtain a correct depth thread.

I have a set of HSS 8mm like that, a bit of a PITA to use, but a very good thread particularly in Stainless.

When I bought them I didn't know they were like that ???

I have a 'normal' set of 8mm too now.

Dave.

EDIT Pic taken sort of !!

Not too good but it's possible to see the difference..

Dave

 

[mklotz]

To allow for depth of thread in determining tap drill size, use the formula:

TD = MD - 0.013*DOT/P

TD = tap drill diameter
MD = thread nominal major diameter
DOT = desired depth of thread expressed as percentage
P = thread pitch expressed as tpi (threads per inch)

Example - 1/4-20 with 55% DOT

TD = 0.25 - 0.013*55/20 = 0.25 - 0.03575 = 0.214 (closest drill is #3)

Slick as deer guts on a glass doorknob.

 

[zeeprogrammer]

Actually tried some toothpaste on a part I was practicing on. Chose a 'whitening' formula and wondering if it's simply more abrasive than normal paste.

'Progressive'...thanks for the name.

Marv...working back and using your formula...I had used a #7 bit and that gives 75% DOT. Why 55%? Experience? Some other criteria?

Thanks.