Author Topic: Motorized turntable for grinding  (Read 259 times)

Anthony Graham

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Motorized turntable for grinding
« on: December 27, 2017, 11:17:49 AM »
One of the big problems with my (sadly incomplete and ruined) 6" mirror project was that I have a small garage and there's barely enough room to walk around my grinding stand. I would like to make a motorized turntable so that I can sit/stand in one place while grinding/polishing. I'm not looking for a Mirror O Matic, just a turntable that spins on its own - kind of like what Gordon Waite uses in many of his mirror making videos.

Does anyone know of any design plans or commercial products I could use for this?



Jay Garcia

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Re: Motorized turntable for grinding
« Reply #1 on: December 28, 2017, 03:03:32 AM »
You might want to look at a "potters wheel". Motorized or manual...manual would most likely be cheaper and IMO would probably work fine.

Look at Craig's list obviously. Also look up some local art/pottery supply places in your area and ask them. Heck, might get lucky and someone might loan you one or let you come over and use theirs.

PS, don't do anything...and certainly don't buy anything without getting plenty of input from the folks here! You certainly don't want more problems with this project and your parents getting even more gruff about the whole thing.

PPS. Building a turn table SOUNDS easy and cheap....but unless you find some EXACT plans that lay down the EXACT parts and the EXACT total cost and EXACTLY how it goes together I would avoid that. DIY builds of any nature tend to be a lot harder and costlier in practice than in theory.

Which reminds me of a favorite phrase:

In theory there is no difference between theory and practice but in practice there is.

adrajacte

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Re: Motorized turntable for grinding
« Reply #2 on: January 03, 2018, 02:51:10 PM »
Quote
(sadly incomplete and ruined) 6" mirror project


I don't believe that your 6" is ruined!

What about a "Lazy Susan" ?
Forget the motors, keep things simple.

A customized simple Lazy Susan for mirror grinding can be build from a sturdy round disk made from plywood + some roller-skate wheels (or similar) put up-side down on a table below. Some kind of vertical axis through a hole in the table and fixed to the underside of the disk to keep it in place.
Simple, easy and cheep to build

Larry Hopkins

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Re: Motorized turntable for grinding
« Reply #3 on: January 10, 2018, 04:48:40 AM »
Good idea lars.

Or for that matter just buy a large lazy susan bearing at the hardware store.

Tyler Cox

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Re: Motorized turntable for grinding
« Reply #4 on: January 10, 2018, 10:04:30 AM »
Hmm. Potter's wheels are expensive (a couple hundred bucks). Think I'll just use a Lazy Susan for now.

Thanks guys!

Shawn Bush

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Re: Motorized turntable for grinding
« Reply #5 on: January 11, 2018, 02:28:19 PM »
I thought of using a lazy susan when I made my mirror this past spring. I have a 12" diameter lazy susan. It would have too much play when you push the mirror back and forth. I want to have the mirror or tool on a firm base. No wobbles, shakes, or shimmies.

I didn't have a stool or bench to walk around, so I just used the corner of my work table. I cut out a piece of 3/4" plywood with a 12" diameter. This way I couldgrind and walk partly around the table, and then walk back around to the starting point, and work my way partly around.

The 12" circle of plywood has a 1/4" counter sunk hole drilled in the center, and I drilled a 1/4" hole in the work bench. I inserted a 1/4-20 bolt thru the circle and thru the bench. The plywood just rests on the table top, androtates as needed.

With this setup you actually can stay in one place, working the mirror, rotating it one direction, and then the circle the other.
Got the idea?

When I started a wet, I would put a little piece of tape on the back of the mirror, and on the circle.If you stand still, you rotate the mirror ccw, and rotate the circle cw. If you work around the table, you rotate the mirror ccw, and then step to the left. Once you start, you won't even think about it, it'll become a routine.


Ryan Chaudhari

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Re: Motorized turntable for grinding
« Reply #6 on: January 15, 2018, 12:07:39 PM »
A powered turntable is nice; if you're handy and can scrounge some parts you can make one for very little and don't have to worry too much about details.Unless a pottery wheel is designed to take a lot of pressure on the outside edge of the platter I doubt it would be suitable.Alternatively, the simple board shown here works quite well for about a 10" or smaller mirror. The one I'm referring to is what the girl is sitting on. It straddles two chairs. The glass is held by a couple of cleats and a wedge is between the glass and a third cleat. It sounds like a pain but you get into a rhythm of grinding, pulling out the wedge, moving the mirror a bit and reinserting the wedge, and you can progress quickly. When you're done with a session put the chairs away and stow the board upright.

Not the only way, but a way.

ruesonecrai

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Re: Motorized turntable for grinding
« Reply #7 on: January 21, 2018, 04:16:10 AM »
Quote
One of the big problems with my (sadly incomplete and ruined) 6" mirror project was that I have a small garage and there's barely enough room to walk around my grinding stand. I would like to make a motorized turntable so that I can sit/stand in one place while grinding/polishing. I'm not looking for a Mirror O Matic, just a turntable that spins on its own - kind of like what Gordon Waite uses in many of his mirror making videos.

Does anyone know of any design plans or commercial products I could use for this?

What's ruined about it?

A turntable doesn't have to be motorized, just turn it or the tool/mirror by hand every few strokes.

When you get this finished, you will be amazed at the results.

Tom Doyle

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Re: Motorized turntable for grinding
« Reply #8 on: January 23, 2018, 05:19:30 AM »
Quote
Alternatively, the simple board shown here works quite well for about a 10" or smaller mirror. The one I'm referring to is what the girl is sitting on. It straddles two chairs. The glass is held by a couple of cleats and a wedge is between the glass and a third cleat. It sounds like a pain but you get into a rhythm of grinding, pulling out the wedge, moving the mirror a bit and reinserting the wedge, and you can progress quickly. When you're done with a session put the chairs away and stow the board upright.

Not the only way, but a way.

I agree with Gary on the simple bench. There's an hour long video of John Dobson on Youtube showing how to build a telescope where you see him using one of these benches.

I participated in a winter weekend outreach activity in February this year and decided to give this setup a try to show folks attending the daytime activity that in addition to observing with telescopes, it's also possible to make one, including the optics. I didn't have a portable grinding benchI could bring with me (I have a big grinding machine in myworkshop) but Ihappened to have one of these small aluminium platforms used to do work in higher areas around the house. So I attached a wood disc assembled with cleats and brought that to the city civic center were the event was held. I ground an 8 inch mirror for about 6 hours over the two day event and found the position surprisingly confortable. I would rotate the mirror in my hands during grinding and, once in a while, rotate the tool on the bottom.

The only thing to be careful about when using one of these setups is to be even more thorough, to prevent inter-abrasive contamination of the work area. Because you are sitting very near the glass and tool, you are getting abrasives on your pants and shirt, which does not happen as much when you are standing in front of a more conventional grinding stand. With one of these sitting type grinding benches I highly recommend you completely change your clothes whenever you change abrasives, in addition to thoroughly cleaning your hands and arms. The better idea is to strip naked, take a shower and change all your clothes before moving onto a finer abrasive.


malralilin

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Re: Motorized turntable for grinding
« Reply #9 on: January 23, 2018, 08:32:15 PM »
Also, on Dobson's video, he had different areas of his backyard for different types of abrasives. When it was time to change abrasives, everything got washed down and rinsed off with a hose.

I have a bad back, so sitting like that for a long time, would be very uncomfortable for me, especiallygrinding and polishing for hours and hours. Foryoung person, it could be very easy and comfortable, andthat's the way Dobson did it.

Once I started making a mirror, I didn't want to disassemble the set up.Extra precautionwould have to be made to make sure, when things were put away, that nothing got contaminated. My wood shop in my basement became my "optical lab". At any time, I could go down and work on the mirror. I also did my testing right there too.My shop became a "lab" for 3 months.

Augustus, maybe there are many more things for you to consider.And you may have already thought of them and more. With it being summer, what temp is your garage?Is the temp consistent? Where are you going to test it? Are you going to grind and polish in the garage, and then go into the house to test it?

Just food for thought, and in no way am I trying to discourage you!

Gary Allen

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Re: Motorized turntable for grinding
« Reply #10 on: January 25, 2018, 02:39:36 PM »
Quote
Also, on Dobson's video, he had different areas of his backyard for different types of abrasives. When it was type to change abrasives, everything got washed down and rinsed off with a hose.

I have a bad back, so sitting like that for a long time, would be very uncomfortable for me, especiallygrinding and polishing for hours and hours. Foryoung person, it could be very easy and comfortable, andthat's the way Dobson did it.

Once I started making a mirror, I didn't want to disassemble the set up.Extra precautionwould have to be made to make sure, when things were put away, that nothing got contaminated. My wood shop in my basement became my "optical lab". At any time, I could go down and work on the mirror. I also did my testing right there too.My shop became a "lab" for 3 months.

Augustus, maybe there are many more things for you to consider.And you may have already thought of them and more. With it being summer, what temp is your garage?Is the temp consistent? Where are you going to test it? Are you going to grind and polish in the garage, and then go into the house to test it?

Just food for thought, and in no way am I trying to discourage you!

The garage stays at a somewhat constant temperature but it probably fluxes by up to 15 or so degrees F. I ground and polished in the garage, using different trash bags covering my grinding stand for each grit. Temperature never became a problem until the day the mirror and lap for the 6" got stuck, and it was close to 100 degrees that day. Never had any contamination problems or scratches.

Not sure where I plan on testing, but it'll probably be in the garage. For the 6" the focal length was short enough (39") that I could've done testing with the mirror and tester at opposite ends of the dining room table to make things easier, but I plan on doing a 10" f/8 next so that wouldn't work.

I do plan on commercializing this if I get good enough, which is the other reason a turntable would be nice.

James Holt

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Re: Motorized turntable for grinding
« Reply #11 on: January 25, 2018, 05:40:25 PM »
I made a lazy susan from scrap, an acorn nut sits on top of the bottom board. The disk sits on top of the nut by allowing it to sit within a drilled hole.

I grind while my kiddo naps. If I were to polish I'd add cleats to the top disk and clamp the bottom board down.


miswalltile

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Re: Motorized turntable for grinding
« Reply #12 on: January 30, 2018, 01:22:12 AM »
Don't leave the mirror on the tool over night. Yep, when it dries out, it gets stuck. Same thing when you polish. If you're not going to polish, keep the mirror off the pitch. It too will get stuck.Youwill becold pressing before you start to polish, anyway. Leaving the mirror on the lap will make the lap thinner and thinner and you'll have to keep opening up the facets.

You may have difficulty in polishing in warm temperatures. The pitch, even it's on the hard side, will be too soft.

In grinding you could get away with a variation of the temp of the room. In polishing, the temp should be stable.

I agree, a turntable would be nice. But maybe at this time, learn making a mirror without one. Going to a turntable will be another learning process. I do like that you're looking down the road.

IMOH, just some thoughts.

James Merrill

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Re: Motorized turntable for grinding
« Reply #13 on: January 31, 2018, 11:07:11 AM »
A board on a couple of supports (like cinder blocks) that slopes a bit downhill to make it drain off the end works really well. I'll even shoot you a pic of what I used a lot back in the beginning. Many mirrors up to 12.5" were hogged, ground, and polished using this board as the worktable, and a lot of that was done outside to avoid contamination. Dobson's different patches of the lawn is a good tip. It started life as a cabinet door (I think) from a discount lumberyard and know it serves as a shop table on top of a bunch of boxes.

You don't need wedges or anything, the key is to have some play in the cleats so they can rotate, like thick rubber hose. You just rotate the mirror a set amount each wet. Very easy.

You can see where three cleats (screws with some hose on the top) were attached, and, in polishing, some sort of pad is helpful to even out the support.




David Knoll

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Re: Motorized turntable for grinding
« Reply #14 on: February 03, 2018, 10:31:54 AM »
My first polishing machine (years ago) had a bicycle wheel on a spindle below powered by a motor spindle pushed up against the tire. It worked; very cheap and it looked cheap too.