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Author Topic: Sources of precision machine parts for concave facetor  (Read 597 times)

FlashGP

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Re: Sources of precision machine parts for concave facetor
« Reply #15 on: October 29, 2018, 06:36:18 PM »
I'm happy enough with the bearings on the allignment layer (y axis) as they are just to allow movement for alligning the cutting mandrel with a line drawn between the centre of the plattern and passing down the centre of the quill.

But the x axis bearings may drum a little so I'll most likely swap them out.

I was going to use a push rod to drive the osvillator, butwas thinking today that a spring loaded push pull wire connected to the oscillator motor will allow the plarform holding the mandrel driver to stop moving without breaking if anything (eg a finger, the quill if the mast is too close, the grand munchkin's finger) jams it.

Regards
Flash GP
Yours Sincerely
Flash (Gordon)

Rusted

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Re: Sources of precision machine parts for concave facetor
« Reply #16 on: November 06, 2018, 07:24:11 AM »
There's a video of an OMF concave machine here, its worth a look for anyone contemplating a build.
https://www.youtube.com/playlist?list=PLSKAi6gpaAXW2kVeCiqc6sILG1YvKU2wE


FlashGP

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Re: Sources of precision machine parts for concave facetor
« Reply #17 on: November 06, 2018, 07:06:32 PM »
Thanks Rusted.  I hadnt seen a Polymetric in operation.  I found and downloaded the patent the other day.  It's interesting to see it has 1 motor driving rotation an dx oscillator.

I was toying with the idea of cutting t he front end off a cheap drill press to serve as the oscillator body, but settled on an easier design for a back yard tinkerer.

If I get it working, I'll post some pictures.

Regards
Flash.
Yours Sincerely
Flash (Gordon)

Rusted

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Re: Sources of precision machine parts for concave facetor
« Reply #18 on: November 07, 2018, 07:14:33 AM »
How do they achieve the back and forth motion? I looked and looked and couldn't figure it.

FlashGP

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Re: Sources of precision machine parts for concave facetor
« Reply #19 on: November 07, 2018, 08:49:45 AM »
The Polymetric looks like it is using an oscillator driven by a worm drive.

The facebook site called woodworking crazy has a wooden oscillator driven by a gear with teeth missing in a 180 degree arg, which sits inside a toothed slot with thhet missing at each end.  As the gear rotates it pulls the slot along in one direction and when it gets to the end, disengages and rmthen engages the teeth on the other side of the slot.  Ingeniois.

But most m achines, including the VJ use an offset pin on a wheel, like the arrangement connecting the piston of a steem loco to its wheels.

VJ and Clarry Trevena drive the oscillator by placing a disk on the plattern.  Offset on the disk is a post with a small bearing on top.  This sits in a slot in the base of the oscillator that sits above the plattern.  As the platten rotates the base plate of the oscillator slides back and forth.  You need a mill to make the parts.

I am achieving the same thing using tie rod ends from Banggood.  These are a bearing mounted on a thread.  I bought a 5mm male RH thread and 5mm female RH thread and screwed them together.  One end will sit on a post on my base plate, the other on a pin on an arm attached to a 30 rpm geared motor.  It is tiny, but should be strong enough to drive the oscillator.  Another option is to use a microwave turntable motor, but these are slower and 240v.  I think it is safer to use 12 or 24v and keep the 240v isolated from the workings.

I am just waiting for my drive motor to arrive to see if it will be quiet enough for my purpose.  I figured the hobby motors and switch mode power supply cost as much as an industrial motor from Motion Dynamics.  If they don't live up to expectations, the 25 amp power supply will still drive 2 x 60w motors so I havent wasted much.  The mandrel drive is a motor with a 5mm shaft for drills and small cnc cutters.
Yours Sincerely
Flash (Gordon)

Rusted

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Re: Sources of precision machine parts for concave facetor
« Reply #20 on: November 08, 2018, 06:41:05 AM »
Flash, you know you can make a very nice 12v power supply from a computer power supply. It's fairly easy as the nice clean regulated 12v is already there you just need to play with the wire that turns it on when you push the PC power button. Plenty of instructions on doctor google.


FlashGP

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Re: Sources of precision machine parts for concave facetor
« Reply #21 on: November 08, 2018, 07:15:36 PM »
Yes,  but I threw out our desktop a few years ago.  Only use laptops now.  This way I can use the power supply to drive heavier motors if these a re too noisy.  I figured $35 for a 25 amp supply pretty good.
Yours Sincerely
Flash (Gordon)

 

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