# Another diamond lapper



## rabler (Jun 17, 2021)

Inspired by @Janderso, I’ve started my own diamond lapping machine.  Thanks to him for the ideas and feedback.

I found a used geared motor, 3/8hp, 3ph, 170rpm on ebay.  Also a Teco L510 VFD, 120v single phase input, for up to 1/2 hp.  This is probably excessive frills, but I’ll get variable speed.

Ordered a 8” diameter disk of 6061, 1/2” sawcut,  for the platten, and a 1/4” x 6” x 12” piece of stainless for the table from McMaster.

The motor has a 3/4” shaft.  I had an odd piece of turned CRS that I turned into a hub.


Turning the aluminum platen was a bit of a challenge.  I wanted the face true with shaft to minimize runout, but I couldn’t thiink of a way to turn the face and bore the hub for the motor shaft in the same setup.

I ended up mounting the hub on the platten first.  1/2” hole in the platten, press fit to the hub. Hub drilled and tapped for 1/4-20, so I can mount a simple center to true the lapping plates, or a washer to clamp the plates if desired although  I expect magnets will suffice.

Turned the face of the platen with the hub clamped in a 4 jaw, and could turn enough of the rim and outside of the back face of the platen so it was true with the front face.  Then I flipped the combination in the 4 jaw and indicated the cut part of the back face as well as the rim of the hub to within a 1/2 thou.  Drilled and bored the hub to a close fit for the motor shaft.




Stll need to broach the hub for a key and drill and tap for a couple of set screws.  Then cut recesses for the magnets.

Haven’t gotten past that in terms of finalized design, although pondering a few ideas.


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## rabler (Jun 18, 2021)

Milled my piece of stainless flat this morning to make the table. One of the ideas that I'm inclined to pursue is to put the table on a pivot so it can be flipped up and back to make it easy to get to the platen to change disks/grits.  Have some rough sketches but need to sit down and work out dimensions to see if it'll work.  Thinking of using a spring pin on either side to secure it in position.


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## Eddyde (Jun 19, 2021)

Looks like a fun project, please post more pictures!


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## rabler (Jun 19, 2021)

A few more pictures...

I’m planning on mounting the vfd as shown, above the motor.

Had an issue with my face mill, top right side of table.  It’s 316 stainless.















Haven’t decided whether this will be benchtop or on a stand like a grinder.


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## rabler (Jun 20, 2021)

Saturday was mostly fab work, built the base.  Square tube is 1 1/4”, base plate is 6” x 3/8” hot rolled. Overkill but it was something I had on hand.    It adds a bit of weight to the base.
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(edited comment: that backplate isn’t twisted, some sort of camera artifact)

The front of the base will eventually get a drip tray screwed to the bottom.



The vertical plate in back will hold the VFD. Holes still needed to mount that. Motor bolts to the bottom plate, which has already been drilled and tapped.  Didn’t get pictures but four shallow blind holes (.625 dia x .210 deep) drilled in the platen for magnets.

Next need to machine arms for the table, and bend a shroud for the VFD.
Still need to broach the keyway in the platen hub too.


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## FOMOGO (Jun 20, 2021)

Good example here by Steve Summers.This 



 was part two of the build. Nice work on yours Randal. Mike


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## rabler (Jun 20, 2021)

Put in some ongoing work in the bathroom remodeling, then took a break to do a bit more in the shop on this project.  Today’s accomplishments were to glue in the magnets, and make the shroud for over the vfd.



I wanted to round the top corners of the shroud, consistent with the round platen.  I did a little math on using a piece of rod as a bending template.  Backed that with some square stock just to make it clamp up right.



TIG welded that to the backplate.



Here’s a test fitup.  VFD isn’t bolted in, so the yellow box is acting as a spacer.



My enclosure will get a front face, but I’ll leave the bottom and upper third of the back open for air circulation/cooling.  The backplate, which the vfd heatsink/case will bolt to, is 1/4 thick so that will also help with cooling.  Open bottom is probably not up to UL electrical compliance since someone could get their fingers under there and touch live contacts, but my shop, my tool.


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## rabler (Jun 20, 2021)

FOMOGO said:


> Good example here by Steve Summers.This
> 
> 
> 
> was part two of the build. Nice work on yours Randal. Mike


Thanks Mike.  It’s a fun project.  Most folks think of it as a carbide grinder, but I’m primarily interested in honing HSS lathe toolbits.  I have a hard time using a small hand hone as I tend to ever so slightly round edges which essentially makes a dull tool.  This should be easier to get a clean angle.


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## rabler (Jun 20, 2021)

Useful thing about this VFD is it will output 3phase at 220V using 120V single phase input.  I believe this 1/2 hp version is the biggest model that Teco makes with 120V input.


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## rabler (Jun 22, 2021)

Used the K&T 3K vertical to clean up a 20” piece of 3/8” x 6” hot rolled to start making the table mount.
400 rpm on a 6” face mill, 10 inserts, 8ipm, .030 DOC.  Went through it easily.
Wouldn’t want this as my primary mill, but when it comes to a big job it really is a fun option.
View attachment IMG_1061.MOV





View attachment IMG_1058.MOV


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## rabler (Jun 23, 2021)

A bit more progress


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## rabler (Jun 24, 2021)

Rough out the pivots. 3/8” round tab fits in the uprights.  The table will bolt to these.  Some sort of 300 series stainless, not easy to machine


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## rabler (Jun 27, 2021)

In case there's any doubt in anyone's mind, 316/316L stainless is a PIA to machine.   Work hardens.  And it produces very nasty little sharp slivers.


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## rabler (Jun 27, 2021)

Table is mounted on the pivots.  VFD mounted.
Still need to make the bracket arms under the table that hold it at various angles.  My design calls for spring pins with holes for every 0, 5, 10, 15, 20 degrees, and a slide lock for arbitrary angles.

Then I need to broach the hub.  Blind hole so a standard broach won’t work, will have to make a spindle mounted broach.

Decided this will ultimately be free standing, so a stand will get fabbed.  Back to the clinic this week so wont be able to make progress for a whike.


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## rabler (Sep 4, 2021)

Got back to working on this today.  Made the two arms for the table.  Interesting rotary table work.  Had to use a fixture plate to get the needed radius on the 6" rotary.  Inside of these is 6" diameter, outside is 9".  I started by cutting the inside and outside curve rotating the table.  Then locked it down and made a pass a cross the top which references to the table bottom.  I had all the hole positions calculated for the DRO, so I drilled those with the mill table, including end holes for the plunge slot.  Then back to turning the rotary table.  I used a 1/4" ball nose end mill, which worked well for this.  The rotary table has a lot of backlash, so light cuts, and using a hand to pre-load the rotary table was necessary.

The slot is for a clamp bolt to pass through.  The row of pins is for indexing on 5 degree increments.  The solitary larger hole is for a cross-brace between the two arms.

The surface finish on these two pieces of metal is horrid, cut from a piece on the scrap pile, must of been playing with face mills and getting chatter?  But I'm happy I got these done without any real mistakes.


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## rabler (Sep 9, 2021)

The table mechanism is done except for some fine tuning/cleanup.
I got carried away with the design, I have both pins (the small knurled spring pin) at 5 degree increments, and a friction clamp for arbitrary table angles.

Next up is a setscrew to hold the hub to the motor shaft.  It is a tight enough fit that I’ve been able to test run without it, but if it starts to slip it’ll wear.   

Then a post/base as I would like this to be free standing rather than benchtop.


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## rabler (Sep 9, 2021)

If anyone wants a laugh here are my design notes.


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## FOMOGO (Sep 9, 2021)

Looks a lot like my design work. As long as the finished product functions as intended, who cares what the drawing looks like. Nice job on the lapping rig. Mike


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## rabler (Sep 21, 2021)

Getting closer to done.  Still needs some final cleanup, and painting.


Stand made from misc stock on hand.  Hex base is 1 1/4" x 1/8" A36 flats, cut to 12" sides (which also gives a 12" radius at the corners).  Angled them in a bit from straight vertical by about 15 degrees for cosmetic reasons, and maybe a little kinder on stubbing toes.  Three of the hex corners have pieces welded to the center tube, threw some 12 ga fence wire in there, and used some leftover masonry from a bathroom tiling project to fill it.  Gives a nice heavy base.  I put a little body putty on there to fill some pinholes and rough spots.


As you can see the table flips back to make swapping disks trivial.  Spring pins secure it in place when in use.  It wasn't an issue on the bench, but now on the stand it really needs a stop to match the spring pin locking position.  Probably need to add a bolt off one side to hang unused discs on.    Also you might notice there is a clamp on the back side holding it on to the base.  UPS just delivered my McMaster order with the longer bolts needed to secure the machine to the stand.



Per @Janderso posts, I may want a tray under the wheel to help with dripping.


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