Granite base CNC router project

[TorontoBuilder]

I have a problem...

The more I look at this granite plate, and run my hand over the surface, the less I want to murder it by installing a bunch threaded inserts to affix whatever work holding system I end up with.

Especially since I've been dreaming of using this for scraping.

So I need another surface plate, that does not need to be so perfect. Or can I effectively still blue up surfaces if my plate holes some holes?

Or since this is pristine surface plate, perhaps I could use use it as a base to cast a "new" epoxy granite base, one that is not 4" thick.

 

[Janger]

How about 1" thick spoil board(s) and use the edges of the granite for threaded inserts? The inserts hold the spoil board to the granite with some sort of supports or bridging. One board with a mounted vise, another board with xy matrix of inserts. etc. A quick attachment method would make it convenient - like how a table saw fence is often so simple to place and clamp.

 

[DavidR8]

Wouldn’t a chunk of granite from a monument company be sufficiently flat?

If it had gouges or other damage sure but since it was calibrated in June seems a shame to use a perfectly fine surface plate for this.

 

[Susquatch]

Wouldn’t a chunk of granite from a monument company be sufficiently flat?

Great plan but seriously flawed. The markup on monument granite is so extravagant that guys buy surface plates to use as monuments....... Apparently death is an expensive way to leave......

 

[DavidR8]

Great plan but seriously flawed. The markup on monument granite is so extravagant that guys buy surface plates to use as monuments....... Apparently death is an expensive way to leave......

Never had to buy one so I have no idea.

 

[Janger]

How about 1" thick spoil board(s) and use the edges of the granite for threaded inserts? The inserts hold the spoil board to the granite with some sort of supports or bridging. One board with a mounted vise, another board with xy matrix of inserts. etc. A quick attachment method would make it convenient - like how a table saw fence is often so simple to place and clamp.

This was fun to model up. I think the big bolt needs a handle more of them 2? 3? 3/4" holes? Note the slot so the spoil board just slides into place.

 

[Darren]

Wouldn’t a chunk of granite from a monument company be sufficiently flat?

They are flat enough for stairs

 

[Susquatch]

The more I look at this granite plate, and run my hand over the surface, the less I want to murder it by installing a bunch threaded inserts to affix whatever work holding system I end up

I've been looking at a 24x36 plate that has been abused. I think it could be had for $500 - maybe less. The trouble is that it's been used to stack stuff on it, has no cert tag, and isn't mounted properly on a 3 point stand. There are also some places where the granite is dull. I don't have the means to check it properly. But I'd be happy to make the guy happy for you.

It's 350 pounds - Double that indexer you grabbed for me.

I'd like a stone that big. I'd also like the stand and the 24" Fowler Height Gage that it comes with. But I'm not paying 500 for an uncertified, poorly cared for, surface place and I'm not trying to make a CNC Router Table.

Just throwing stuff out there.

 

[Susquatch]

They are flat enough for stairs

View attachment 54264

You robbing graveyards now Darren?

 

[TorontoBuilder]

Great plan but seriously flawed. The markup on monument granite is so extravagant that guys buy surface plates to use as monuments....... Apparently death is an expensive way to leave......

Oh dude, I know where there are thousands of granite slabs just sitting around, doin nothin in a place as quiet as a graveyard. free for the taking and 99% of them wouldnt be missed

 

[TorontoBuilder]

This was fun to model up. I think the big bolt needs a handle more of them 2? 3? 3/4" holes? Note the slot so the spoil board just slides into place.

I have my side rails attached to the sides.

But If I just attach a vacuum plate from the perimeter I still have a lot of free area.

Or since I am casting the side rails I can cast in place thru holes for spoil board/vacuum plate attachment

 

[TorontoBuilder]

I've been looking at a 24x36 plate that has been abused. I think it could be had for $500 - maybe less. The trouble is that it's been used to stack stuff on it, has no cert tag, and isn't mounted properly on a 3 point stand. There are also some places where the granite is dull. I don't have the means to check it properly. But I'd be happy to make the guy happy for you.

It's 350 pounds - Double that indexer you grabbed for me.

I'd like a stone that big. I'd also like the stand and the 24" Fowler Height Gage that it comes with. But I'm not paying 500 for an uncertified, poorly cared for, surface place and I'm not trying to make a CNC Router Table.

Just throwing stuff out there.

I got my pristine recently certified 24x36 plate and stand for $100... so no, I refuse to pay more than $200 for a less pristine model

 

[Susquatch]

I got my pristine recently certified 24x36 plate and stand for $100... so no, I refuse to pay more than $200 for a less pristine model

This is one of those times we need to be able to use multiple reaction Emojii. LMFHO, IN LOVE, JEALOUS, WOW.


Trade you?

LMFAO!

 

[PeterT]

I would not bite into a perfectly good granite plate drilling for inserts or whatever. Just seems wrong on multiple fronts but maybe that's me. Your idea of using it as a perfect mold surface has merit IMO. You arrange an array of threaded inserts, vacuum channels, rebar tubes (= mass reduction & rigidity enhancers)... or many kinds of other custom features into an assembly from which you cast a dedicated fixture table. You just have to be super careful about the releasing aspect because sticking would be a bad thing. Rather than trusting a releasing agent applied to the granite (deep rabbit hole subject) you might be able to find a suitable film. These products can be amazingly accurate in terms of dimensional thickness consistency. I'm not quite sure what you are after in terms of accuracy but I would think would meet most vacuum requirements.

 

[TorontoBuilder]

I would not bite into a perfectly good granite plate drilling for inserts or whatever. Just seems wrong on multiple fronts but maybe that's me. Your idea of using it as a perfect mold surface has merit IMO. You arrange an array of threaded inserts, vacuum channels, rebar tubes (= mass reduction & rigidity enhancers)... or many kinds of other custom features into an assembly from which you cast a dedicated fixture table. You just have to be super careful about the releasing aspect because sticking would be a bad thing. Rather than trusting a releasing agent applied to the granite (deep rabbit hole subject) you might be able to find a suitable film. These products can be amazingly accurate in terms of dimensional thickness consistency. I'm not quite sure what you are after in terms of accuracy but I would think would meet most vacuum requirements.

View attachment 54303

well there is one other opinion that tells me I'm not totally out in left field.

I wish I had a better memory, because I did see a youtube video about casting onto a near perfect reference surface, and I seem to recall that they may have used a film as a release agent rather than a wax based product.

I like the idea of cast in place vacuum channels, most excellent. I'll need to think about how to make a fitting that can be placed in the mould and remain secure during the fill, tampering and vibrating stage and yet release very easily. I have to think about that part.

Of

 

[PeterT]

A common way to tack the array of threaded inserts down is just glue them to the release face with similar compatible adhesive as used on the main pour. So thickened, fiber reinforced epoxy is good. Grout a fillet around the perimeter & release film or wax protecting the threads so the main pour does not encroach into threads. The insert ODs typically have a knurl or thread which the adhesive bonds to. Usually strong enough but sometimes inverted T-nuts are used.

^This^ method is typical for mold flanges where the layout path may be curved or irregular & layout doesn't matter because the opposite side will be pre-located with its corresponding bolt or dowel. If you need linear spacing precision for matching linear jigs or fixtures then a better system is required. I have seen pre-threaded bars for example so you just have have to get the inter-bar spacing correct.

You have touched on a good point, some kind of vibration is often used to conform the particles within the slurry & also de-aerate during cure depending on lots of variables. This can complex if you have structural framework within the pour. But vibration really on depends on end result if this is warranted & to what degree. If you showed me some example end result fixtures we could take it from there. (My experience is with composite layup molds).

Best to make something small as a test specimen representative of the big pour so you figure out the 27 things 'surprise' beforehand. First & foremost, you dont want even a pinhole leak of your film to encroach on the granite & also wise to apply release to the granite as insurance

 

[TorontoBuilder]

A common way to tack the array of threaded inserts down is just glue them to the release face with similar compatible adhesive as used on the main pour. So thickened, fiber reinforced epoxy is good. Grout a fillet around the perimeter & release film or wax protecting the threads so the main pour does not encroach into threads. The insert ODs typically have a knurl or thread which the adhesive bonds to. Usually strong enough but sometimes inverted T-nuts are used.

^This^ method is typical for mold flanges where the layout path may be curved or irregular & layout doesn't matter because the opposite side will be pre-located with its corresponding bolt or dowel. If you need linear spacing precision for matching linear jigs or fixtures then a better system is required. I have seen pre-threaded bars for example so you just have have to get the inter-bar spacing correct.

You have touched on a good point, some kind of vibration is often used to conform the particles within the slurry & also de-aerate during cure depending on lots of variables. This can complex if you have structural framework within the pour. But vibration really on depends on end result if this is warranted & to what degree. If you showed me some example end result fixtures we could take it from there. (My experience is with composite layup molds).

Best to make something small as a test specimen representative of the big pour so you figure out the 27 things 'surprise' beforehand. First & foremost, you dont want even a pinhole leak of your film to encroach on the granite & also wise to apply release to the granite as insurance

View attachment 54305

I'll design up a framework and proposed mould and post it here.

 

[Tom O]

Back in school while on detention we repaired the school desktops with a wooden frame holding some plastic from a dry cleaners bag I think. The plastic was made taught with a hair dryer and the height was controlled by nails on the side of the desktop the frame would rest on. The resin was poured and the film kept it flat. The plastic peeled right off.

 

[Bandit]

Well it appears I made a "grave" mistake the other day when I was at the local picking transfer site (garbage dump), there were some head stones laying in the concrete junk pile. Replacements it appears as some corners were broke off, some edges chipped, etc. No, none had my name on them!!!
The thought did cross my mind,(didn't take long, small area), maybe a good simple close enough for some jobs surface plate. Alas, I did not even take one. Next time maybe.

 

[PeterT]

Releasing agents/films are a subject unto themselves. Flat surfaces are relatively easier than curved but you still need the right product. Often a release agent is also applied to the film especially if the film has some adhesion to the tool body. If the pour exotherms during cure, the film must be tolerant of this temp or else it can wrinkle or distort. Should not be an issue with the correct type of epoxy in an aggregate / sand recipe but can be in large mass sections. Sometimes a single pour must be done, in other cases it can be or must be done in stages in which case the correct time is very important.