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Old 15-02-2021, 06:44 AM
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mura_gadi (Steve)
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Grinding Table

Hello,

I recently scored a three draw bedside pine unit I am converting to use as a barrel to grind on. What sort of surface coating should I use on the top to help avoid trapping grits. I was thinking of using a clear drying PVA glue and piling it on fairly thick - Top, sides and the cleat holes possible the underside too if my 1ltr of PVA will go the distance.

So far I have ripped the top off the unit and I'm making a removable 50cmx25mm plywood disc to sit on top - I want to be able to hose the top down between grits. I have screwed the draw units into the frame to add rigidity into the unit. The bottom draw I have cut the back out of to place sand bags and gym dead weights into for extra weight as well as add a thick piece of plywood to take all the extra weight.

I was going to use dowel on my cleats to hold the mirror and use a separate set for each grit. The holes for the dowel would also be lined with PVA glue as a seal to stop the plywood layers trapping grits. Would I be better off just nailing the cleats in and filling in and recoating the smaller nail holes between grits, rather than the reusable holes for the dowel option? The top has be planned to be able to be fixed and removed from the unit without breaking the top surface of the plywood disc with screws/nuts/nails/holes etc.

Is this a good approach, is there a better option, are there better sealers to use, without busting my meager funds. The PVA is water resistant only and I have no idea how damp my under lying cloth will get tbh. I plan on 1-2 hour grinding session with the top be allowed to dry between uses.


Thanks
Steve
Ps. The pine unit was a road side pickup, the disc I have measured and planned but not executed yet so, I haven't fully committed to the top yet.

Pps. I want to be able to make anything from 8" to 16" mirrors on the grinder table over its life time. The reason I baulked at the dowel, was I may have some slurry/grits leak into the top draw, which may present problems for contamination between grits. However the draw should be sealed against drafts etc when the top is in place.

Last edited by mura_gadi; 15-02-2021 at 10:33 AM.
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Old 16-02-2021, 07:35 AM
Rod
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Hi Steve

I'm not sure I fully follow how you intend to use dowels but I'm sure what you are suggesting will work as long as the pine unit is a comfortable height and sturdy enough not to wobble.

I would just keep it simple for your first mirror. Some screwed in cleats covered with a few layers of newspaper will work. Just discard the newspaper between grits. That will do a lot of the cleaning for you. I recommend formply as the base for your top. You get it from Bunnings. It's a plywood used for working with concrete and has a thin phenolic resin coating on both sides. It's easy to clean and you won't need to coat it. It's also cheap.

After you've made a mirror you will develop ideas about how you want to work in future. For example a motorised turntable running at 3 to 5 rpm is easy to build and makes the process easier.

If you want to make a top that can handle different sized mirrors then you could get some ideas from reading P34-39 of this manual:

http://mirror-o-matic.com/conversion...conversion.pdf

Hope that helps,

Rod.
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Old 16-02-2021, 03:55 PM
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mura_gadi (Steve)
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Hello,

Sorry the dowel was to hold the glass in place while I grind. I have three lines 120 degree apart from center. Thought I could just drill holes along those lines for various mirror diameters using the dowel as plugs. The dowel as braces to avoid the mirror moving, with the dowel about 3/4 up the side of the mirror.

The idea was pretty much the pdf, but I was working on three lines, the cleats were the wooden blocks, I just wanted dowel as I could keep them in sets for the grits(and lot cheap than nuts/bolt washer combo's). Changing the face on the blocks/cleats for different size mirrors is fairly simple with a 1" face+. Wasn't keen on dragging previous parts to the next grit any way I could cheaply.

But I am probably over thinking it as you do with a new challenge, before you've even started.


Thanks for the reply and link
Steve

Last edited by mura_gadi; 16-02-2021 at 04:11 PM.
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