Author Topic: This had me scratching my head for a while...  (Read 3700 times)

Offline cfellows

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This had me scratching my head for a while...
« on: December 02, 2017, 10:11:05 PM »
So, this little piece had me puzzled for a while today. 



It's the blade advance screw from my little Stanley block plane.  You can see that it has two different diameters and the larger diameter threads into this carrier which notches into the bottom of the plane blade.



I've seen these kinds of devices used in the past where threads of two different pitches are used to provide a finer movement than a single thread could provide.  Here's how the assembly fits into the plane body.



Both threads are right hand and the smaller, threaded end screws into the plane casting.  The larger diameter, which has a finer thread would let the blade carrier advance, but at a rate determined by the difference between the two thread pitches.  By careful measurement, I determined that the screw advanced about twice as fast as the blade carrier which would indicated that the smaller diameter had a pitch twice as coarse as the larger diameter.

Now the whole point of this exercise was the fact that the threads in the cast iron body were stripped, so I wanted to drill it out, loctite in a new piece, then drill it out and tap it since the screw part is in good shape.  But, when I measured the thread with my thread gauge, it was 28 TPI, same as the larger diameter.  That's when I decided I had moved to an alternate universe.  They couldn't be the same pitch, or the mechanism wouldn't work, the blade and carrier would stay in the same position, no matter how much I turned the screw. 

It took me almost an hour to finally figure out that the smaller diameter was double threaded.  That is, it had a double start thread, so the pitch was actually 14 TPI.   :facepalm:  I expect finding a double start tap is going to be a bit of a problem.   :thinking:
So many projects, so little time...

Offline Florian Eberhard

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Re: This had me scratching my head for a while...
« Reply #1 on: December 02, 2017, 10:38:42 PM »
Hi Cfellows

Just glue in an already threaded sleeve, then you can cut the douple start thread on the lathe. (use the compound slide parallel to the lathe bed and then move it half the pitch when the first thread is finished)

And I guess it would be best to also thread that sleeve on the outside, this should increase the strength of the bond (A thread has more surface than a simple sleeve)

Florian

Offline 10KPete

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Re: This had me scratching my head for a while...
« Reply #2 on: December 02, 2017, 10:42:14 PM »
Chuck, I looked at the pics and read the article. Then had to go back and look at that thread again before it sunk in that I was looking at a double start thread!!

I have quite a few Stanley cutting tools but never noticed that. The urge to go look is getting stronger....

Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Offline cfellows

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Re: This had me scratching my head for a while...
« Reply #3 on: December 02, 2017, 11:14:24 PM »
Hi Cfellows

Just glue in an already threaded sleeve, then you can cut the douple start thread on the lathe. (use the compound slide parallel to the lathe bed and then move it half the pitch when the first thread is finished)

And I guess it would be best to also thread that sleeve on the outside, this should increase the strength of the bond (A thread has more surface than a simple sleeve)

Florian

Thanks for the suggestion, Florian.  Unfortunately, using my lathe to cut an internal, double start thread inside a 5/32" diameter hole is a bit beyond my capability, not to mention current tooling.  Setting the compound parallel to the spindle axis, however, is a good idea.

Chuck
So many projects, so little time...

Offline crueby

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Re: This had me scratching my head for a while...
« Reply #4 on: December 02, 2017, 11:17:57 PM »
All the hours and hours I've used my Stanley low-angle plane, and I never noticed that it had two threads, let alone a double-start one, on that knob.

 :shrug:

Hope you get it sorted, those are handy planes. Fortunately there are still versions being made if no luck rethreading it.

Offline cfellows

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Re: This had me scratching my head for a while...
« Reply #5 on: December 02, 2017, 11:27:19 PM »
Well, Gents, you are looking at what i would have thought beyond my capabilities 2 hours ago...



I decided to try making my own double start tap.  I started with a 1/4" diameter drill rod and turned the end down to 5mm, which is the measured diameter of the threaded screw.  Then I set up my lathe to cut 14 TPI and cut that thread in the end of the rod.  Next, being careful to maintain the axial position of the part, I loosened the chuck and turned the part 180 degrees, then retightened the chuck.  I could have accomplished the same thing by using Florian's suggestion of setting the compound parallel to the lathe spindle axis.

Finally, I cut another 14TPI thread exactly halfway between the existing threads.  When I tried my threaded rod in what's left of the threaded hole in the plane body, it screwed through effortlessly.   :DrinkPint:  So, now I'll cut some axial grooves in the threaded rod to make it into a tap and see if I can make a threaded sleeve.

Chuck
So many projects, so little time...

simplyloco

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Re: This had me scratching my head for a while...
« Reply #6 on: December 02, 2017, 11:42:08 PM »
Excellent! Not an easy thing to do.
John

Offline Kim

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Re: This had me scratching my head for a while...
« Reply #7 on: December 03, 2017, 12:03:51 AM »
That's pretty cool, Chuck!  Can't wait to see how it all works out for you!
Kim

Offline 10KPete

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Re: This had me scratching my head for a while...
« Reply #8 on: December 03, 2017, 12:44:02 AM »
 :ThumbsUp: :ThumbsUp:

 :popcorn: :popcorn:

 :cheers:

Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Offline cfellows

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Re: This had me scratching my head for a while...
« Reply #9 on: December 03, 2017, 01:56:15 AM »
Thanks, guys, I'm happy to report a successful conclusion to this project.  Here is  picture of the threaded sleeve...



Although I'm more than happy with the results, I can't say it was a walk in the park.  The main issue was that I should have made the tape about .010" larger in diameter.  The threading went pretty smoothly, but the screw fit was way too tight.  Luckily, the brass tube had a thin enough wall that I was able to run swage the tube by running the screw in and out several times.  It actually expanded the tube diameter by about .005".  But I got the threaded tube loctited into the plane body, got the plane put back together, tuned up, and it works great.  The thread fit is snug, but it turns freely and will do the job nicely.

Chuck
So many projects, so little time...

Offline steamer

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Re: This had me scratching my head for a while...
« Reply #10 on: December 03, 2017, 03:28:53 AM »
I made a 0.217-40 tap recently Chuck.   I cut some flats at the end of the tap    It cut wonderfully.

I posted a thread on it.....I'll dig it up

Dave

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Damned ijjit!

Offline steamer

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Re: This had me scratching my head for a while...
« Reply #11 on: December 03, 2017, 04:00:17 AM »
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline cfellows

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Re: This had me scratching my head for a while...
« Reply #12 on: December 03, 2017, 06:11:53 AM »
http://www.modelenginemaker.com/index.php?topic=7288.110

It's in my Levin thread   page 12

I found your pictures in the thread.  Gotta say, I'm kind of surprised that geometry would cut very well.  But, nothing succeeds like success!

Chuck
So many projects, so little time...

Offline cfellows

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Re: This had me scratching my head for a while...
« Reply #13 on: December 03, 2017, 06:15:00 AM »
By the way, the block plane that I was repairing was a Stanley 60 1/2, like this:



Chuck
So many projects, so little time...

Offline 10KPete

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Re: This had me scratching my head for a while...
« Reply #14 on: December 03, 2017, 08:59:36 AM »
Yep, I love that plane. Lives in my back pocket when fitting doors... 

Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

 

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