What one earth is the Artful Bodger making now?

[John Hill]

Doesnt look like the usual Madmoddeer stuff!

I can see a light bulb, some glass things, a switch, some sort of coil and what looks like an old speaker magnet, lots of wire too!




Oh no!  That is a computer sitting on there!



That looks a bit out of place in the lathe!



Uh oh, theres that Gyro Gearloose stuff and whats that stuck to the feed screw?

[boxtriker]

Well looks like you have a couple of magnetic suitches where as well ok i give up what you up to !!!!!!!!!!!!

[bogstandard]

Methinks we are getting ready to calculate out the accuracy of the threading charts.


So most probably a pulse generator in the chuck, and a counter on the leadscrew, or something along those lines.

You are attempting to get the exact ratios between the two rotating parts. Then because you already know the pitch of the leadscrew, you will be able to calculate out the TPI or pitch of the thread being generated to a very accurate percentage.

I am now preparing myself to get shot down in flames.

John

[John Hill]

Exactly right of course Mr Bogstandard!

I did a few 'runs' today,  the chuck switch gives 15 signals per revolution and the magnet on the lead screw gives one per revolution.

There are two reed switches on the lead screw, one is to stop and start the counting at the same point in the shaft's revolution and the other is the actual revolution count sensor.

I ran the rig for 10 revolutions of the feed screw and recorded the spindle revolutions,  I did each test three or four times and in each case got at least three identical counts.  So I was pretty pleased with the consistency.

The figures are quite close, for example A2 came out as a metric pitch of .747 and A4 a pitch of .598 (they are on the tables as .75 and .6 respectively).

What I cant resolve is that none are exact and I am sure there should be at least some...

There is probably a fault in my logic somewhere, maybe the old and much dreaded "one out error" somewhere, seems that my brain just does not work like it used to.  (If you are ever offered radiation treatment it might be best to write your address down first so you can at least find your way home.)

[bogstandard]

John,

This was what I was on about before, only keeping within a percentage tolerance.

My Atlas lathe was a great example. Because of the large quantity of change gears and combinations you could put onto the quadrant, very tight ratios could be produced, and with a little mechanical calculation, you could get it to cut almost any metric or imperial thread, so they would match up with a third party thread very accurately.

Because this machine we have has so few quadrant setups and change gears, even though there is a large combination of internal headstock gearing, you just won't be able to get the very finer tolerances.
Basically we are stuck with what the machine will allow.

It all looks great on the advertising literature, but not too good when it comes to the physical side. What they should do is tell you what the thread tolerances are as well.

So it won't take more than half an hour for you to check every thread combination shown on the charts, so I will look forwards to seeing the actual thread sizes generated. It will save me hours doing it manually. 

What a nice man, dropped himself right in it there.


But joking aside and in all honesty, great job.


Bogs

[sbwhart]

Well done that man what a great bit of bodging 

        

Your having fun arn't you Bodger   

Cheers

Stew

[John Hill]

Thanks Stew.

Bogs, you would not believe that I initially tried studying the parts list in the 'manual' to determine what the possible ratios might be.... scheesh, there are a lot of little cogs in there!

Still, I find it rather strange that there are not some that come out as exactly right so I doubt my method somewhat.

According to the 'manual' there are 42 combinations (presumably from the A1.. E5) which means there are eight pairs of duplicates and I have only found two so far.

Today is Sunday and I will need to devote time to preservation of the pair bond, maybe a bit of time on the project this evening.