Author Topic: GRBL Multi-Axis Grinder  (Read 478 times)

Offline dave benson

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GRBL Multi-Axis Grinder
« on: July 26, 2020, 12:44:59 pm »
I thought I would start this thread as I've finished with the a Drilling and Tapping plugin.
Bubba I led you astray, The spindle connection is a B16 taper not a thread like the other
chuck at the back of the pic. It's a RHOM chuck and after a cleanup runs smoother
than either of the two Sanou ones, one of which was still in its box, although at some stage
it has sat in water and had some light surface rust.

This left me with with a bit of a dilemma as what to do as with the spindle mount .
I wanted to use the big chuck for the cam grinding and use the collet chuck for the
smaller dia 3 mm wire.

I decided to make a miniature Backing plate (in Cast Iron) in the style used in lathes and make an
adapter plate for the Drill chuck and one for the collet chuck.

I've got to this stage in the pictures the backing plate was light pressed onto the shaft
with super bearing mount Loctite (left overnight), then the securing bolt thread was machined and inserted
and then the facing and register were done last.


Dave

Offline dave benson

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Re: GRBL Multi-Axis Grinder
« Reply #1 on: July 28, 2020, 12:35:38 pm »
I've finished as much of the Spindle as I can for the moment, The little face plate's
work well, I've bored the Spindle nose to take the Angular Contact bearing (5201 2RS)
it has the same Bore and ID but is 15.9 mm wide compared to the 6201's 10 mm
light duty electric motor bearing that was in the Drill press, these bearings have quite
a bit of internal clearance and in my opinion a poor choice for that application.

The bearing should arrive in two or three weeks, so I'll continue on tidying up the
XY stage, and the two rotary axes it sits on.
I've also moved the grinder base plate over 150 mm to give a bit more room for the
last rotary axis in the stack (C) to be able to rotate another 60 degrees.
This also allows the grinder to use Diamond profiling wheels as well as the cup wheel.

Just for curiosity's sake, to see how much clearance was in the bearing (the 6201)
 I assembled the spindle and clamped it down to my mill table and checked it with an
indicator and at 50 mm along the linear shaft and 140 mm from spindle snout, the
clearance measured 0.8 mm.

The other major source of error will come from the grinder bearings themselves
so I found  some 19 mm SS shafting and may have to make a belt drive spindle
to drive the cup wheel with a couple of tapered roller bearings, driven from one
side of the bench grinder and on the other side a wire wheel.

Dave

Online Bubba

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Re: GRBL Multi-Axis Grinder
« Reply #2 on: July 28, 2020, 14:16:59 pm »
Nice solution Dave. Well done!
My 2¢

Win 10 64 bit, CB [1.0} rc 1 64 bit, Mach3, ESS, G540

Offline dave benson

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Re: GRBL Multi-Axis Grinder
« Reply #3 on: August 12, 2020, 13:45:05 pm »
I got a little time to today, and mounted the grinding wheel
to see how the layout looked, and  with the ER 11a collet chuck
things looked good, however the Drill chuck just looked like it
had too much overhang and would not be that rigid, being that long
and canter levered like it is it'll act like a tuning fork.

So I bit the bullet and ordered a ER 16 collet chuck with a 150 mm X 12 mm
shank  with the same  ID as the AC bearing.
It's a little less capacity (10 mm) than the 12 mm of the chuck,but I can live with that.

The original spindle shaft is 12 mm at the bearing  surfaces and the rest is
necked down to 10 mm so with the collet integral to the shaft and the whole
shaft is 12 mm along it's length, and having the end of the work piece 40 mm away
from the bearing instead of 120 mm it'll be more rigid.

The Bill of Materials so far is:

3 x Nema17 92 oz\in steppers.
1 X Nema 23 Sanyo Deki Step-Syn for the spindle.
1 X Nema 23 387 oz\in.
1 x ER16 Collet chuck  with 150 mm shaft + a collet set 1 to 10 mm.
2 x 5021 2RS AC bearings + Three tapered Roller Bearings + 50mm Thrust Bearing.
1 x Mks Gen V1.4 Controller Remix Main Board W/ Usb Cable For Mega 2560 Ramps 1.4.
5PCS 3D DRV8825 Stepper Motor Driver+Heatsink.
1 X five metre length of GT2 Belt, plus 10 X  20 tooth Drive Pulleys.
5 x GT2 Idler Timing Pulley with Bearing 20T 5mm Bore.
2 x GT2 Pulleys 60 teeth 5 mm bore. I'll bore it to 12 mm.

I've loaded the 5 Axis version into my test mega and have been taking GRBLGRU
for a test run (GRBLMachine  wont display the rotary axes) so for testing and debugging
GRBLGRU is better, but you could use GRBLMachine to send the code or just
run it of the SD card.
I note that you could also use G2Core on a Due 32bit 84 MHZ Controller as well, which
has Six Axes. There's also a STM32 version with 500khz step rate.

What I have will be fine as the Axes are very short compared to a router,mill ect.
I have drilled and tapped the holes for a sixth Axis if needed just in case.

We are in stage four lockdown now, so no moving about and to boot a couple of
mail distribution center workers  caught covid, so they have reduced the staff by
30 percent which may cause delay for the stuff I've ordered.

While I'm waiting for the stuff to arrive I'll model all the motor mounts, and try to
make the drive system as compact as possible.
The motors and drivers have arrived today.

The photos are of the Foot mount\C Axis Bearings  mount\XY stage and Spindle
mocked up to see what the center height needs to be.
I made the Foot and bearing mount from cast Aluminium, the rest is CRS.
It turned out nice,but took a long time to do as the stock was nearly at final
dimension and I had to make a mandrel and a fixture.
Dave

Offline EddyCurrent

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Re: GRBL Multi-Axis Grinder
« Reply #4 on: August 12, 2020, 14:53:15 pm »
Marvelous stuff Dave !
Made in England

Online Bubba

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Re: GRBL Multi-Axis Grinder
« Reply #5 on: August 12, 2020, 16:34:24 pm »
What Eddy said! Nice.
My 2¢

Win 10 64 bit, CB [1.0} rc 1 64 bit, Mach3, ESS, G540

Offline dave benson

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Re: GRBL Multi-Axis Grinder
« Reply #6 on: August 15, 2020, 04:17:47 am »
Thanks guys, it sure ain’t no looker being made from what I had on hand, but it is functional.
In the pictures, the first one is of the bearing cover highlighted, the second one of the two faces
that were lapped to give a very close fit without touching each other.
Why?

Well the stepper motors have 92 oz/in holding torque and with the gear ratio it'll be 276 oz/in.
So not a lot, and the Slip\Stick phenomena caused by the seals actually comes into play especially
with an 32 mm seal. this is because static friction will be greater than the dynamic friction.
Anyway this C Axis set up (a revolute joint) must be as free to move as possible so no seals.
The bearing in the top has a plate cover with a gasket and the bottom has a bearing cap that is partially
submerged in the carrier plate with a radial clearance of 0.03 mm then the partials have to go around a 90
degree corner and through two wide flat surfaces that have been lapped together.
I don't know what the gap is but it's very small as the method to produce it was like this.

Machine the surfaces leaving enough meat so that when assembled the unit is locked (I left 0.05 mm)
but this was a bit much because when lapping what you do is lap the bearing surfaces then assemble
the unit and put the right preload on the bearing and test to see if it has freed up, if not then disassemble
the unit and lap again rinse and repeat, and as I left to much material on this took a long time to achieve
a clearance fit.

When I assemble it for the last time I'll put a bit of way oil between the lapped surfaces as well.
It's not a seal really but a dust excluding device  and I will use a elastic sock made out of very thin neoprene rubber
to completely surround the joint.

The C Axis moves very freely when assembled and preloaded and with no slip\stick that I can feel.
I'm very much looking forward to getting the pulleys and belt to give it a run.

Dave

Offline dave benson

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Re: GRBL Multi-Axis Grinder
« Reply #7 on: August 20, 2020, 13:21:33 pm »
A small update.
I got the motor mount with integrated belt tensioner done today.
It had to translate along the X axis to align the pulleys.
It had to rotate 180 degrees to move the motor from one side of the spindle
to the other, this allows to spindle to swing closer to the grinder spindle allowing
a more acute cutting angle.
It had to adjust the belt tension.
There is a small lever that adjusts the belt tension that I won't put on until
the belt and pulleys arrive. It's made for a 200 tooth belt and has adjustment for
15 teeth so could accommodate a 210 tooth belt with room for adjusting it.

Dave

Online Bubba

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Re: GRBL Multi-Axis Grinder
« Reply #8 on: August 20, 2020, 23:48:21 pm »
Dave, you making great progress. Keep the pictures coming.
My 2¢

Win 10 64 bit, CB [1.0} rc 1 64 bit, Mach3, ESS, G540

Offline dave benson

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Re: GRBL Multi-Axis Grinder
« Reply #9 on: August 30, 2020, 13:50:03 pm »
Another small update.
None of the ordered parts have turned up yet, but soon I hope.
I've added another Axis to give the grinder some nod, so that I could sharpen endmills
and drills, I'm aiming for a factory grind for drills not the grind you sometimes get with
after market Drill sharpeners.
At first I was going to mount the Grinder itself on a pair of stanchions, but this didn’t really
give enough  adjustment and was a bit unwieldy.
So I bit the bullet and made a nodding axis to be fitted to the Axis Stack, Although not
shown here I will make up a locking mechanism for the time being until the rest of the
order comes in.
The head gives +- 20 degrees which will be enough to do most things I want to do.
I've made provision for two types of spindle, Position and Velocity mode. (Separate spindles)
Position mode for most things (the hooks I want to grind and end mills ect) and velocity mode for
contour grinding items held in a fixture type  mechanism.
Dave

Offline dave benson

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Re: GRBL Multi-Axis Grinder
« Reply #10 on: September 10, 2020, 10:12:50 am »
Another small update.
The GT2 Belting and some of the belts and some of the pulleys have turned up.
Also the Ramps 1.4 board has arraived and I've updated the firmware and tested it out
with the appropiate settings for the grinder. It's a very nice board allowing the use of 24 volts
without modification and the stepper drives (they are mactched to the motors) work well.

I also made a spindle nose extension to cover the AC bearing and made a shield for the rear bearing.
I tested the nodding head Axis out to see if the motor had enough holding torque to over come the
friction built into the axis bearings which are steel backed split steel bushes for  the bores are normally reamed
for a free running fit, however in the case this would be unsuitable for a grinder like this, and I have reamed the bore
a little under size to snug up the clearance. If you don't do this the looseness in the fit will translate to the surface
finish of the ground part.

I'm out of gas at the minute so can not braze the fitting sitting on the guard, this is for a water reservoir for a wicking system.
I ran the numbers on the required RPM for this wheel and it worked out at 1400, if the wheel was a 5 inch\125 mm wheel
then it would be a little under 3000 RPM, I'll wait until I've tested out the grinder motion system first before buying the
motor.

Dave