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Author Topic: Prototype Concave Cutter  (Read 640 times)

FlashGP

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Prototype Concave Cutter
« on: January 02, 2019, 05:21:39 PM »
I finally finished my budget concave cutter.  I have embedded links to photos in the Gallery.  click on the link to view them.
http://aussielapidaryforum.com/forum/index.php?action=gallery;sa=view;id=9017

I don't have a lathe or mill so designed the cutter to be adjusted in the y Axis (the mast moves in the X axis).  There's 25mm of play each side of centre.  This means that I can cut parallel lines on the side of a step cut by moving the mast out of alignment for cuts other than the first.  The adjuster thread advances 2mm per turn. I used anti backlash nuts on the threads to remove the slop in them.

The parts cost me between $450 and $500 to make, before cutting mandrels.  I used linear bearings to support plywood decks that sit around the platten on my Factron.  I used 4mm T Nuts to pressed into the Ply as ancker points, although the lower bearings and alignment screw are sitting on 3mm angle aluminium. 

I made the arm on the oscillator motor from a piece of 10mm square mild steel, drilled, tapped and cut down.  3 taps at 10mm, 15mm and 20mm from the centre means that I can adjust the throw on the oscillator between 20mm and 40mm to accommodate different mandrel sizes.  The link is two tie rod ends for CNC Cuters, one male and one female.
http://aussielapidaryforum.com/forum/index.php?action=gallery;sa=view;id=9020

I bought a cheap Ryobi laser level and Stud Finder at the post Christmas sale.  The laser level throws the laser in a vertical arc so it produces a line on a surface.  Here I'm using it to sight down the middle of the cutting mandrel and shine on the mast.  If the cutter is out of alignment, two lines appear on the mast as in the picture, as the cutter is brought into alignment they merge into one bright line.  I'm pretty sure this has something to do with the reflection from the curved surface of the mast.  Once the mast is aligned, the Quill is lowered and the Quill Stop adjusted until the laser is shining down the centre of the Quill.
http://aussielapidaryforum.com/forum/index.php?action=gallery;sa=view;id=9021
http://aussielapidaryforum.com/forum/index.php?action=gallery;sa=view;id=9025

I used a 25 amp switch mode supply with 2 10 amp pulse width modulators for speed control of the cutting motor and the oscillator drive.  I only needed a 10 amp supply, but the price difference means was small and I can use the Power supply to drive larger motors in need.  The motors I am using only pull 4 amps between them.

http://aussielapidaryforum.com/forum/index.php?action=gallery;sa=view;id=9023
http://aussielapidaryforum.com/forum/index.php?action=gallery;sa=view;id=9024
One of the PWM modules is reversible, it is the one standing on edge, the other cost $3.60 and I am trying it out.  It seems to work OK.  I had to de-solder the Pot on that  module and add 3 signal wires so I could mount it as the box I purchased was a little small.  The resistor in the photo is a 10w 22 ohm power resistor to keep a 1/2 amp current flowing.  This is to stop the power supply going into overvoltage when the motors are turned off.  All up the Power supply cost me almost $100 and  it has the grunt to drive 2 x 90w motors.
« Last Edit: January 02, 2019, 06:09:14 PM by FlashGP »
Yours Sincerely
Flash (Gordon)

Rusted

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Re: Prototype Concave Cutter
« Reply #1 on: January 02, 2019, 06:33:13 PM »
That's good to see Flash, I looked at those little gear motors and wondered if they would be suitable for driving the oscillating motion.
I'm still tossing up options and not even remotely close to putting anything on paper let alone building it.
Great work

FlashGP

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Re: Prototype Concave Cutter
« Reply #2 on: January 02, 2019, 06:59:33 PM »
Thanks Rusted,


The little geared motor works fine to drive the oscillator.  However I am not sure how long it will last.  I'm going to buy a spare just in case, with shipping they cost under $15.  A microwave turntable motor is only 2W, but 240VAC.  It's safer to use a 12v DC motor.


If the oscillator speed is turned down, the motor stalls if the carriage hits something.  Hopefully this will prevent serious injury if a finger gets in the way, or the stone runs off the end of the Mandrel.


regards
Flash
 
Yours Sincerely
Flash (Gordon)

MakkyBrown

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Re: Prototype Concave Cutter
« Reply #3 on: January 02, 2019, 07:43:35 PM »
Nice one flash :), will have a better look later.
We are a family of 4 from Southern Tasmania.

FlashGP

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Re: Prototype Concave Cutter
« Reply #4 on: January 02, 2019, 11:58:18 PM »
Thanks Makky,


I've managed to tune it so the cutting mandrel runs parallel to the direction of travel by adjusting the bolts holding the motor bracket.  I also placed a shim under the front of the motor bracket so the dial indicator barely moves when the unit oscillates but with the motor turned off. 


The body of the ER11 Collet chuck spins with very little error, but when a mandrel is placed in it, the mandrel runs out and vibrates the dial indicator.  I may have to out the body of the collet chuck in a lathe and make sure the taper holding the collet is running true.


I've ordered a second collet chuck to see if it makes a difference.  Otherwise I'm pretty happy with it.


Let me know if you have any queries regarding it.  The cost of a patent is too great for the anticipated market, but I'm happy to share the idea with anyone wanting to make one. 


happy faceting
Gordon
Yours Sincerely
Flash (Gordon)

MakkyBrown

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Re: Prototype Concave Cutter
« Reply #5 on: January 05, 2019, 12:49:19 PM »
Thanks Makky,


I've managed to tune it so the cutting mandrel runs parallel to the direction of travel by adjusting the bolts holding the motor bracket.  I also placed a shim under the front of the motor bracket so the dial indicator barely moves when the unit oscillates but with the motor turned off. 


The body of the ER11 Collet chuck spins with very little error, but when a mandrel is placed in it, the mandrel runs out and vibrates the dial indicator.  I may have to out the body of the collet chuck in a lathe and make sure the taper holding the collet is running true.


I've ordered a second collet chuck to see if it makes a difference.  Otherwise I'm pretty happy with it.


Let me know if you have any queries regarding it.  The cost of a patent is too great for the anticipated market, but I'm happy to share the idea with anyone wanting to make one. 


happy faceting
Gordon

It might be the mandrel, would be unlikely to be collet. What rpm are you testing at, could the error be being caused by an out of balance mandrel/or out of balance collet chuck?
We are a family of 4 from Southern Tasmania.

FlashGP

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Re: Prototype Concave Cutter
« Reply #6 on: January 07, 2019, 10:32:54 AM »
Hi Makky,

the mandrel runs true in the chuck of my bench drill.

I wrapped a single layer of alfoil inside the hole for the base of the collet holder. 

This removed some of the vibration by redicing the gap between the collet holder and motor shaft, but the wobble on the mandrel is far greater than the vibration on the outside of the mandrel holder.

I have a second mandrel holder on the way and will see if I get similar results with it. 

I was going to borrow a dial indicator from an engineer mate to check for concentricity in the collet holder.  It would only take a high spot to throw it out.  But I realised I can check this with the dial indicator on my mast by setting the cutting angle to 90 degrees.

Am thinking that if the shaft play is the cause of my woes, I may need to drill and tap 3 allignment grub Screws at the opposite end of the motor shaft holder.

regards
Gordon
Yours Sincerely
Flash (Gordon)

MakkyBrown

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Re: Prototype Concave Cutter
« Reply #7 on: January 07, 2019, 10:59:05 PM »
Was just thinking, did you buy the collet separate to the chuck/holder? I think there are a couple of types of ER11 collets/collet nuts. Might be type A and type B.
We are a family of 4 from Southern Tasmania.

FlashGP

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Re: Prototype Concave Cutter
« Reply #8 on: January 09, 2019, 06:56:09 PM »
Ah, yes,

I bought the 1/4 and 1/8 inch collets separately from the collet holder and nut.  They had run out of sets of 1 to 7mm collets and collet chuck.

Gearloose's shaft on his mandrel is a full 1/4 inch so the 1/4 inch collet is a snug fit.

I couldn't fit the collet into the flange inside the collet nut so bored out the flange si I could assemble the unit. 

I have an ER11A on order.  Will see if that improves things.
Yours Sincerely
Flash (Gordon)

FlashGP

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Re: Prototype Concave Cutter
« Reply #9 on: January 09, 2019, 10:25:07 PM »
Hi Makky, my ER11A arrived in today's post along with a set of 1 to 7mm colletts.


The 1/4 inch collett snapped into the new collett nut and I don't know how to get it out.  The Collett nut fits both the ER11 and ER11A collett holder so it shouldn't matter.


The motor shaft fits into the end of the ER11A collett holder neater than the ER11 collett holder, but the tooling (cutting mandrel) wobbles about 1 to 1.5mm at the end when put in the new ER11A collett holder.  An allen key held at continuous sections of the collett holder produced a it of chatter and the end of the collett holder also seems to be wobbling a bit.  I suspect concentricity of the bore for the motor shaft is the issue here, (assuming the taper is ground concetrically.


When I put the old ER11 collett holder back on the motor shaft with the new collett nut and 1/4 inch collett, the tooling did not appear to wobble.  Changing the tooling produced a smaller visable wobble than the ER11A.  Backing off the nut and rotating the collett and tooling before re-tightening the nut seemed to cure this issue, but there is a small amount of chatter. 


This ER11 Collet holder is the original collett holder that I ground out a little using some 1200 sandpaper wrapped around the 1/4 inch collett and pushed into the spinning taper.  I did this to make it release the collett easier after I had drilled out the flange inside the collett nut that pushes the collett out of the taper as you unscrew the nut (because I didn't know better and it seemed too small to allow the collett head to pass through it and mate with the taper inside the front of the collett nut).


I have still to take some measurements and see where the problem lies, but I think it is: 1. allignment of the chuck on the motor shaft, and 2, high spots inside the taper.


Regards
Flash
Yours Sincerely
Flash (Gordon)

MakkyBrown

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Re: Prototype Concave Cutter
« Reply #10 on: January 10, 2019, 09:40:26 PM »
"The 1/4 inch collett snapped into the new collett nut and I don't know how to get it out. "
They do lock in pretty well, rightly or wrongly I push the end of the collet sideways and they usually pop out. Being new might be harder. Might be worth considering upgrading to a cnc spindle, just need to find one suited to lower rpm and cheap.
We are a family of 4 from Southern Tasmania.

FlashGP

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Re: Prototype Concave Cutter
« Reply #11 on: January 11, 2019, 08:36:32 AM »
Hi Makky,
It's a thought, but if I change, it'll be to one with a morse taper.
I have a mate who is a fitter and turner who is talking about sleaving and boring out the hole for the motor shaft to 0.01mm larger than the shaft.

I'm hoping to find a solution that doesn't need access to a lathe so the design can be built by anyone.  Im contemplating putting 3 grub screws in the collet holder so the slop at the end of the motor shaft mounting can be used to adjust the centring of the taper for the collets.

Regards
Gordon
Yours Sincerely
Flash (Gordon)

MakkyBrown

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Re: Prototype Concave Cutter
« Reply #12 on: January 26, 2019, 10:01:08 AM »
How's the machine going FGP? Looking forward to seeing some finished stones.  ;D
We are a family of 4 from Southern Tasmania.

 

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