Author Topic: Screwcutting drop in dial revisited  (Read 9952 times)

bogstandard

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Screwcutting drop in dial revisited
« on: March 31, 2009, 07:35:50 PM »
Some one said the other day that I could write a post about brewing a cup of tea. Well this post is going to be like that.

I did a post about my screwcutting dial

http://madmodder.net/index.php?topic=870.0

This is bringing that post to a final conclusion. But as a separate issue.

You may ask, why do I need a resettable zero point?

When you buy an imperial lathe, the screwcutting dial just has one gear on the bottom, and the zero mark is usually set up at the factory by use of shims on the holder. So in use, the marks drop in the correct position and everything is in sync with the leadscrew.
With a metric machine, you change gears for each pitch range of threads you cut. So normally, you would put the correct gear on the bottom of the dial, and play about with the gear position to realign the zero mark. By doing this mod, no matter where the gear is on the shaft, a few seconds and I can realine the zero drop in point. Also I have locked all three gears on my shaft, so gear realignment isn't possible.

I am doing this post separately because it also shows that things don't have to be spot on, and even jobs on the RT can be 'winged' if you want to.

Starting out with a ruler and a bit of stainless sheet, I did a quickie sketch up of what was required.




The sketch was transferred onto the blued up plate. I could have gone the hard way, and cut and filed it all up by hand. But I have the facilities to take all the hard work out of it, so decided to go down that road. Anything for an easy life.




So what follows is a rough and ready bit of machining, no precision measuring, just cutting to lines with a 'that will do' attitude.
So an 8mm hole was wacked thru the plate at the pop marked position.




Using rough and ready materials, I made up a mandrel to fit the plate onto.




If you notice, even the bolt is a low tensile throw away job from the bitsa box. This mandrel will be thrown away after it is finished with.




This will be a plunge thru and cut away job, so I want nothing coming loose. The whole lot was assembled with loctite.




This was the only precision bit on the job. The RT was zeroed up in X&Y and also the scale was zeroed.




An engraving bit was mounted into the collet, and the plate rotated in the chuck so that when I moved it in the Y axis, it followed the line and ended up at the small hole marking I had put at the outside. The chuck was then fully tightened with the mandrel standing proud enough, that when I would be cutting, the cutter wouldn't hit the chuck jaws.
A line was then engraved from the edge of the mandrel to the small hole position. After that, a centre drill was spotted thru at the hole position.




Turn the RT thru 90 degs, and wind the table in the X until the drill was about midway between the two outer lines, the central hole was then drilled and another hole at either side at 10 degrees offset either way from the first hole. RT rotated to 270 degs and the same thing again.




A 3mm slot drill was plunged thru in the same position as the holes that had been drilled (180, 270) and the RT fed 10 degs either way. This operation made the two curved slots that are required.




A larger cutter was fitted and the job moved in the X axis until it was off the plate. The cutter was fed to depth, and brought in from the side until it met the edge of the outside circle. The RT was then rotated either way until the outside was cleaned up to where I wanted it. The tool was then plunged in and the inner cut done. This needed to be started and finished at a point close together, to provide maximum support of the ring being cut out until the very final bit. Maybe I should have done that on the back, but my original idea was to have a pointer sticking out, it was later that I decided I didn't like the look.




You can just see the plunge and extraction point for the cutter, either side of the engraved line.




The part was snipped away from the mandrel, and the mandrel was thrown away, it has no further use.
After the original zero mark was removed and the part given a rough trimming, it was tried for size. That will do me.




This is after a bit of filing and dressing up. I also made a thumb push knob from a bit of 6mm SS rod. The small hole was drilled thru and a countersink put on the back.




A couple of wacks with a big hammer had the knob rivetted in position.




I now needed a couple of finger screws, so a bit more 6mm rod, a little turning and knurling had them ready to be threaded. That was done with a 3mm die.
BTW straight knurls for tightening & undoing, diamond pattern for gripping.




Finished bits ready for fitting.




After drilling and tapping a couple of holes, here is the finished article on the machine.
It works a treat with all three gears. Taking only seconds to realign the zero position.



Before anyone asks, the chuck on my RT is a self centring four jaw, NOT independent.

I hope you have enjoyed my little foray into non precision machining. At times, things can be done this way, and it makes a nice change from number crunching


Bogs
« Last Edit: March 31, 2009, 07:48:34 PM by bogstandard »

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Re: Screwcutting drop in dial revisited
« Reply #1 on: March 31, 2009, 08:05:38 PM »
Junno John, I was wondering how you'd gotten that there shape for the dial doodad!!?    Forgot to ask you on sunday  :doh:


All is now very clear.... Very nice!  :thumbup:


I will do my best to store that for future use, dunno where or when but it's bound to be a useful way of thin plate holding and working at some point  :)



Nice write up  :thumbup:




Ralph.
I know what I know and need to know more!!!

Offline Bernd

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Re: Screwcutting drop in dial revisited
« Reply #2 on: March 31, 2009, 10:20:21 PM »
John,

Another nice bit of info.  :thumbup:

I'm amased at the things you come up with. Very ingenious. Looking forward to more short projects from you. :clap:

It's not so much the projects I enjoy but the technique you use to get to the result. Thanks much for taking the time to show us John. :bow:

Bernd
Route of the Black Diamonds

bogstandard

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Re: Screwcutting drop in dial revisited
« Reply #3 on: April 01, 2009, 02:09:06 AM »
Bernd,

Most problems have a solution.

If you can't find the solution, give it to someone else to do.


Bogs


Offline SPiN Racing

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Re: Screwcutting drop in dial revisited
« Reply #4 on: April 01, 2009, 02:11:03 AM »
Very Cool... Now to research how to use the threading dial... and stopping the lathe while cutting a point, backing out slightly, running backwards, and then forwards again slightly deeper etc etc... works.. but I will read up on the dial.. so I may go down that road of the dial and gear/dial changing on it.

Very nice quick project :)
SPiN Racing

Offline jemglen

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Re: Screwcutting drop in dial revisited
« Reply #5 on: April 01, 2009, 03:35:05 AM »
Great job John, and an interesting insight into the different uses of knurling.

Your explanation and pics were a joy as always. Wish I had: a. your skill, b. devotion to the job, c. imagination to come up with so many enjoyable projects  :bow:

Jerry

bogstandard

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Re: Screwcutting drop in dial revisited
« Reply #6 on: April 01, 2009, 05:17:25 AM »
Thank you gents for the kind words.

Unfortunately that will be it on projects for a while. I have some work come in over the last few days, and one of them is a rather large project in itself. See attached pics.

It was made sometime in the late 60's by an old model engineer, who has been a long time pushing up daisies. A Marcher slide valve engine, and has been used and abused for the last few years. I am having to give it a good dose of looking at, make a few replacement parts, and get it retimed in so it will last for another 40 years.

Not one to be shown as project material, as it will take all my time sorting it out.

John

Just a bit about my knurl quote. :hammer:

Quote
straight knurls for tightening & undoing, diamond pattern for gripping

What I said isn't a hard and fast rule, just one that is generally accepted. You do things as you see fit, with the tooling you have to hand. :thumbup:

I can just imagine everyone rushing out to buy straight knurls, all because I said it was the way to do it.

As I have said before, the way how I show it is my way, you might have different solutions.
« Last Edit: April 01, 2009, 05:43:13 AM by bogstandard »

Offline sbwhart

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Re: Screwcutting drop in dial revisited
« Reply #7 on: April 01, 2009, 05:34:41 AM »
Thats an interesting engine John I'll have a look at that next time I'm round

Stew
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Re: Screwcutting drop in dial revisited
« Reply #8 on: April 01, 2009, 12:21:01 PM »
Quote
one of them is a rather large project in itself
.... Looks tiny!!   :lol:     :doh: 


I thought from your description of the engine it was going to be complex and full of intricate parts....  :jaw:    :) 

A few pics....? No need for a major write up John.... Just a before (you've done that above) a middle (in bits) and an end (soon to be loverly and shiny ehh?)

Would that be a possibility?   :thumbup:




Looks like you might be a little busy..... But I'm still going to aim for a week day off soon, see if I can't get you to that scrappy   :)



Ralph.
I know what I know and need to know more!!!

bogstandard

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Re: Screwcutting drop in dial revisited
« Reply #9 on: April 01, 2009, 12:40:13 PM »
Ralph,

Externally maybe, but inside has a lot more going on as well.

No bling on this one required, just a clean down. It should look exactly the same on the outside as it does now.

We will see.

Just hope the scrappies hasn't had a clean out just before you come.

John

Offline Darren

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Re: Screwcutting drop in dial revisited
« Reply #10 on: April 01, 2009, 01:21:52 PM »
Interesting looking engine you have in your hand there John
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

bogstandard

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Re: Screwcutting drop in dial revisited
« Reply #11 on: April 01, 2009, 03:18:10 PM »
Yep, must be worth somewhere around a grand now.

I have a similar one to be built sometime.

Bogs

Offline SPiN Racing

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Re: Screwcutting drop in dial revisited
« Reply #12 on: April 05, 2009, 12:51:32 AM »
Wow thats a very very cool looking little piece of kit there.

You do get some interesting stuff to play with!!!
SPiN Racing

bogstandard

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Re: Screwcutting drop in dial revisited
« Reply #13 on: April 05, 2009, 03:50:55 AM »
Spin,

Bits 'n bobs like this come thru the shop fairly regularly, but this one has a little more work on it than normal.

It is no different to what you do, I am sure I would be amazed at some of the stuff you get up to.

Bogs