Experiment Engraving Machine Dials

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awemawson:
Bill, no I don't think that this one does :(

Anyway the plot thickens

I wanted to prove if the error was actually consistent, and measure it more accurately. So I set up a 'zero pointer' (*) and wrote a diddy program to turn the 4th axis 20 turns or 7200 degrees so that the error would be magnified and more easily measured.

Odd results: first two runs at 2000 degrees per minute gave errors of 37 and 38 degrees added to where we should be - so close that I thought that I'd perhaps bumped the scriber holder when taking the picture.

But I then repeated the test of 7200 degrees but halved the speed to 1000 degrees per minute, and got a result of 31 degrees :bugeye:

... so it's NOT consistent and could well be a dim bulb in the encoder (I think that they use an under run pea bulb) or it could conceivably be a pulley or shaft slipping.

A bit of dismantling tomorrow if I can find time

Turns out to be about 0.527% so the original guess at 1/2% wasn't too far off

(* I'd have used the inbuilt fidicule marker if I'd remembered that there was one :doh: )

John Stevenson:
It's probably on last years British summer time.

Encoder leaving here on Saturday, clearly marked "Please throw underarm "

awemawson:
John you are a hero :bow:

:thumbup: :thumbup: :thumbup:

awemawson:
so bright and early this morning I set it going at a crawling 100 degrees a minute for the 7200 degree test, then went and cleared out the pigs, cooked my porridge, ate it, and returning to the workshop it was ALMOST there :ddb: (an hour and 12 mins of course)

... how did it do, well it still over travelled but by less at 29 degrees.

So no choice but to start pulling the thing apart, a diversion I could well do without. Swarf cover off, and even so getting the end cover off the belt drive was a pain ... who designed this .... :scratch: (me!)

Eventually got the bits obscuring the belt cover off to reveal a toothed pulley on the end of the servo motor with a grub screw only finger tight :bang: I was tempted to put the pulleys back with Loctite as well as grub screws, but future dismantling would be almost impossible without destroying the alloy pulleys.

So I decided to drill and tap them both for a second grub screw at 90 degrees to the first - this is where things started to go awry :( Trying to undo the (hard of access) grub screw on the encoder, the ball end of my (cheap and nasty Chinese) ball ended allen key decided this was the time to break off inside the grub and jam there forever :bang:

However I managed to gently tap the pulley off the shaft, then as the grub screw / broken ball end proved too hard to drill out, put two new grubs in and ignored the old one. I put a reamer through to take the slight protrusion of the old grub screw which would have stopped the pulley going back on.

(These are tiny M3 grubs with 1.5 mm hex sockets so a bit delicate.)

So having jumped through those hoops it was just a case of putting it back together making sure the pulleys were aligned and the belt tensioned and trying it out.

..did it work ..... :scratch: ...you bet :ddb:

SORTED

Now perhaps I can get back to making that bally dial that revealed this issue :lol:

John Stevenson:
Clumsy bastard.

Still sending the encoder as it's no good to me

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