The Adventures of Jim's plane's Smaller Brother

[Richard T]

Yes Andy - spot on.

The last hope with these tools is to thread it from scratch (or not). I'll have to order some new muscles.

This will show once and for all whether the tap and/or die are duff.

 

[jimi43]

Hi Richard

I think Andy may have a point...I think you may have altered the final profile of the Acme shape:

This would mean that you've exceeded the tolerances for the side angle either at the top or bottom or both.

I'm not entirely sure (though I would need to check) that the Norris threads were pure Acme...but they were probably cut on a lathe as "square" thread...

This thread subject seems so simple but can go on for years!

Still...that aside...it looks beautiful! Glad you've also got over your fear of through rivets!! =D>

Cheers mate

Jimi

 

[Richard T]

Thanks Jimi - Yes, Norris are square, 14 tpi which I would very much prefer it's just that the acme tools are available and cheap.

As for the thread cutting entirely on the lathe I will need a lot of practice: my first ever screw cutting attempt you see above.

The second go I had was done with the tool ground narrower and not as deep - I'm pretty sure I did not 'go over' with it but as Andy says, the only way to find out will be to do the whole thing with the die.

 

[Dave D]

I have to confess that I advised Richard to screwcut a groove first then finish with a die.
I have always cut large threads this way to ensure an accurate thread form.
How about measuring every dimension of the tap using a micrometer or digital caliper and comparing with Jimi's chart above
to see if that is the culprit?

 

[Richard T]

Very sound advice it was too Dave and I'm sure that when I virgin cut the bar with the die it will yield the same result. I need to put a bit of an angle on the end first - starting it is going to be fun. (hammer)

If it is the same I'll ring the supplier up and ask "is this normal"?

 

[xy mosian]

I need to put a bit of an angle on the end first - starting it is going to be fun.

Couldn't you start the thread as you have done, just to start the die, and then cut off the duff bit?
xy

 

[AndyT]

I suppose there is a strong possibility that the "matched" Acme tap and die are aimed at someone wanting a loose fit for something such as a clamp that you would spin down rapidly then tighten a final half turn for clamping - and are not designed to make a backlash-free fit at all.

 

[Dave D]

That is an excellent thought Andy.
I have been driving myself nuts trying to come up with an explanation
Yours seems to be the best idea so far.
Measuring the tap should reveal if you are right.

 

[Richard T]

It was fine with a nine degree taper on it xy - I threaded it in the raw and it's exactly the same.

I think you could be on to something too Andy. I'll have a go at measuring the tap later on.

 

[rxh]

I think the plane looks great - I like the bold styling and the spiky bits. I'm following the acme thread discussion with keen interest. I've never tried cutting one - I hope you get the problem sorted out.

 

[xy mosian]

I hesitate to stick my oar in, being only an interested onlooker. If you spend some time measuring bits etc. and then lathe cut a screw thread you have a one-time solution. Is there any posibility of using the existing die, set at half cock, to make a new tap? This would be an exact match, what is more there would be some adjustment available to trim the feel of the action. A lathe would be needed to prepare the tap blank, before threading, and a milling machine for the swarf slots. Tempering might be tricky but as a blacksmith you have the secret of FIRE. A matching tap and die would give you a many-time solution.
xy

 

[Richard T]

That's a very good idea xy - I know someone who might be able to do it ( helped me with The Thing in the Garage).

Other than that I have been thinking that I really need to get my screw cutting skills up but first, my tool grinding skills.
If I could turn square threads I wouldn't need to rely on dumbed down tolerances on ready made tools.

Though I think I will go ahead and see how I get on with putting a head on one of my woeful screws as a bit of a practice and then at least I will have something to test it with when I get the pivots in.

 

[xy mosian]

Richard, it is very obvious, to me at least, that you enjoy the challenge as much as anything. Same here with smaller bits. The enjoyment's the thing, that and keeping the brain ticking over.
xy

 

[Dave D]

I have just remembered my 1943 copy of Machinery's Handbook so I looked up Standard Acme Thread.
In the small print I found the following.
" For feed or lead screws where backlash or end shake are objectionable the nut is tapped first and then the screw is threaded to fit.
The screw and nut so made are kept as a pair."
This seems to imply that the thread form as designed has considerable backlash built in.
So my suggestion of using a die was not so good after all. Sorry Richard.
This would mean that to cut a male thread would require a form tool ground to an exact fit in the tap
and very carefully creeping up to a depth of cut giving a good fit

 

[Richard T]

Thanks rxh - not everyone likes the spiky bits. It's just that when you follow a cupid's bow to its extreme you end up with the spiky bits. They follow the forward thrust of the handles I feel.

Quite right xy, keeps the brain ticking over. If I ever master infill planes I don't know what's next ... alchemy?

Thanks Dave - acme was never a traditional choice, as far as I can see its main purpose is for lead screws and the easy engagement of half nuts but I will stick with this one.

Yesterday I got on with something that I am more used to; filing the rivets down.







Before I started on this caper, if anyone had suggested that the dovetailing was the easy bit I would have larrrfed. It is though, after a bit of practise.

 

[rxh]

Richard,
There are a lot of clips on acme threads in youtube - if you search on: acme thread cutting.