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Sanity check on milling pockets into MIC 6 tooling plate.

XOIIO

Plastic
Joined
Oct 7, 2021
Hi all, new to the forum though I've heard a lot about it, I'm not a machinist but have a project with a relative who's an apprentice, and wanted to run this past you guys to see how feasible it would be before ordering more parts.

I'm working on making an admittedly overkill upgrade to the print surface of my 3d printer that will be carried forward to a full custom build someday. (unless I go for a larger size.)

The end goal is to be able to use removable flexible plates, but also have the precision surface to mount pei sheets, or use use on it's down, without any mounting holes or thick magnetic sheets that could affect flatness.

So, I'm hoping to mill out about 24 pockets into the 6.35mm tooling plate, leaving a 1.5mm gap between the high temp magnets themselves and the surface. These will be backed with some steel to increase the force they apply, then all capped off with a 500w heater. There's also going to be a few holes tapped for actually mounting. These will have threaded rods with some red loctite, so they're really only single use.

I wanted to check this over though, as it is removing a fair chunk of material from the sheet, and I'm not sure if milling that much out could cause some issues or warping. From what I understand there shouldn't really be any internal stress since it's a cast plate, but I wanted to be sure.

I know of other people who have milled shallower pockets in from the front, but that obviously means that the top surface isn't that ultra precise flatness that you pay for with tooling plate.


If it's of any help here are a couple pictures of more or less what the layout will be. I had been wanting to use round magnets, but with these bar ones there's a discount and I should be above 250lbs of force across the entire surface with said 1.5mm gap, stronger if I could get it down to 1mm, though that feels perhaps a little too close for comfort.

The first plate I ordered looked like Freddy Kruger handled it before shipping, so I do have a practice section we can use but I'd love to hear thoughts from you guys about this project.

LaqEvM5.jpg

Wl0MvHV.jpg



edit: So with 24 of them backed with steel at a 1.5mm gap it should be 291lbs of force, assuming full strength on a fairly thin spring steel sheet, or 391lbs if I could actually get only a 1mm gap from the top surface. Perhaps 1.25mm and ~335lbs is a good compromise, again assuming that's not too thin of a section that might cause weird warping issues when being machined or heated.
 
+ on what Thermite says.

Stresses in cast materials tend to be primarily due to cooling gradients. Generally thin sections and the outside cool faster than the deep innards.

Stresses in rolled, forged and extruded materials are due to working stresses imposed when the material is formed into shape. The harder you have to work in the forming process the greater the stresses. Which is why cold formed material always has greater locked in stress than hot formed. Has to be pummelled harder.

Given nice slow cooling cast material retains very little locked in stress. Overly fast cooling or localised chilling to produce hard areas can produce considerable stresses. Enough to fracture undersized sections.

As stress generally concentrates towards the outer skin of the material the golden rule is to keep the component as symmetrical as possible and, when in doubt, start with something over thick and carefully remove the outer skin.

Hafta accept that sometimes it will bend however careful you are.

I'm convinced that the Chief Gremlin puts special, hidden to human eyes, on the stock material sections that will bend so the gremlin minions make sure I get more than my fair share!

Clive
 
So, this thing won't be undergoing any massively fast cooling or heating, the 500w heater will be fairly quick but I won't be going above 140c, and it will just cool down in room temp air when it's done.

No clue where I'd send it for touch up grinding if it did warp, or to what extent it could warp.

This isn't any insanely high accuracy printing or anything, so some slight warping probably wouldn't even be noticeable, though going over the surface with a dial indicator after would be neat to check it and compare to the old setup, though from what I understand mirror tile should be pretty good flatness wise too. I suppose I'd have to polish it down to get the surface perfectly smooth as well if I did want a glass lie finish on the bottom, though the milling marks would likely make for good adhesion, they'd also make it a little tricky to clean thoroughly.

I just figured I'd go overkill on it right now. I just don't want to end up totally ruining $80 of material, not to mention the 60 ish I think it will be for all the magnets. Unfortunately where I am in Canada there's nowhere local for the stuff.

Basically I figure give myself a really good base for printing that can give me really good accuracy after building up linear rail based machine instead of guide rods, and at that point, the flatness difference of glass vs tooling plate might be decently noticeable .
 
Please define what “flat” means to you and acceptable distortion might be.
What kind of heater?
Over what area is it being heated?
6mm aluminum is not very thick and you’re talking about dumping 500W into it…. Granted it will also come to equilibrium faster.

In my day job, we have thermal engineers to look at thermal effects and distortions, but we are talking about holding positions in nanometers and Angstroms and in high vacuum…
 
Well, love the term shiney-wood lol.

Unfortunately up here everything is really spread out for industrial stuff like this hence having to order the tooling plate from multiple provinces over.

The 500w heater is a silicone pad type that's going to cover the entire base using some 3m adhesive that's pre-applied, and it's going to be PID controlled with a solid state relay. I usually won't be taking it above 80c and it should be pretty darn steady.

In terms of flatness, I'm not sure specifically but apparently borosilicate glass that hasn't been precision ground down can vary as much as .2mm cross the surface, but another factor is that it can warm weirdly when being heated, bowing down in the center and lifting at the corners is apparently a thing when heated on print beds. I know I've definitely had issues printing close to the edges of my bed before because of small inconsistencies, and this bowing behavior would definitely explain why I can lay down .1mm just right in the center area, but have trouble further out.

The old heated bed is an aluminum substrate pcb at 24v and a fraction of the wattage, as well as being thinner, so its heat up time is really awful, and I'm sure it's not very even either.

Assuming there's no issue with the steel backing on one side of the magnet being thicker than the other section, I'm hoping to bridge the gap between the magnets and the heater with said steel section so that its as close to as flush with the bottom of the tooling plate as possible. The high temp magnets will obviously have a different conductivity for heat, but that should at least help prevent these spots from being significantly cooler than the surrounding areas, though they are fairly small sections overall.

From what I found this plate should have less than .38mm deviation across the surface, though I think that's the alcoa spec, and this plate didn't come with alcoa plastic on it, in fact only one side had any protective plastic on it. The new one should supposedly be here today and they say they ordered in new material, so perhaps it will be alcoa stuff. The milling marks on it look pretty much identical to alcoa stuff I've seen images of.

As mentioned I do have that test piece, but it's all fucked up on a few sections of the surface, and it would be a lot of measuring before, machining, then measuring after to see if all that work did twist it up.
 
Hi all, new to the forum though I've heard a lot about it, I'm not a machinist but have a project with a relative who's an apprentice, and wanted to run this past you guys to see how feasible it would be before ordering more parts.

I'm working on making an admittedly overkill upgrade to the print surface of my 3d printer that will be carried forward to a full custom build someday. (unless I go for a larger size.)

The end goal is to be able to use removable flexible plates, but also have the precision surface to mount pei sheets, or use use on it's down, without any mounting holes or thick magnetic sheets that could affect flatness.

So, I'm hoping to mill out about 24 pockets into the 6.35mm tooling plate, leaving a 1.5mm gap between the high temp magnets themselves and the surface. These will be backed with some steel to increase the force they apply, then all capped off with a 500w heater. There's also going to be a few holes tapped for actually mounting. These will have threaded rods with some red loctite, so they're really only single use.


I wanted to check this over though, as it is removing a fair chunk of material from the sheet, and I'm not sure if milling that much out could cause some issues or warping. From what I understand there shouldn't really be any internal stress since it's a cast plate, but I wanted to be sure.

I know of other people who have milled shallower pockets in from the front, but that obviously means that the top surface isn't that ultra precise flatness that you pay for with tooling plate.



If it's of any help here are a couple pictures of more or less what the layout will be. I had been wanting to use round magnets, but with these bar ones there's a discount and I should be above 250lbs of force across the entire surface with said 1.5mm gap, stronger if I could get it down to 1mm, though that feels perhaps a little too close for comfort.

The first plate I ordered looked like Freddy Kruger handled it before shipping, so I do have a practice section we can use but I'd love to hear thoughts from you guys about this project.

LaqEvM5.jpg

Wl0MvHV.jpg



edit: So with 24 of them backed with steel at a 1.5mm gap it should be 291lbs of force, assuming full strength on a fairly thin spring steel sheet, or 391lbs if I could actually get only a 1mm gap from the top surface. Perhaps 1.25mm and ~335lbs is a good compromise, again assuming that's not too thin of a section that might cause weird warping issues when being machined or heated.

Machining those pockets out isn't going to make the plate warp, your not removing any significant amount of material, plus MIC6 is stable in my experience.

Not sure what your definition of "ultra precise flatness" is? It's going to be good enough for a 3D printer now dought. I've seen some plate, that seems to be flat if you put a precision straight edge across the plate, but when you run your (calibrated) fingers across the plate you can feel the subtle troughs ridges, which doesnt suggest to me "ultra precise flatness"

As for the plate looking like Freddy Kruger, next time you buy plate specify the plate has to be free of dings/gouges/scratches You can get that plate from McMaster, their material is ussually clean.
 
plus MIC6 is stable in my experience

Generally yeah.. I had a piece of 18"x18", I think it was 5/8" thick.
It had a few little things cut into it. It sat leaning up against the
side of a shelf for quite a few years..

Just leaning.. Maybe at a 15 or 20 degree angle, over time put about an .008" bow
in it.. I didn't expect that.. Now it all gets stored flat.

-----------
Thought: Looking at all those little pockets all in a nice line, something
in my brain is telling me that that is a bad idea.. If there is any stress,
I'm guessing you are going to get a bend right across each one of those lines..
I'd stagger them, or kick them over at a 45, do something to keep the spacing
you need, but I wouldn't want all those pockets in a line..

I have zero scientific theories to prove what I'm saying, just something in
my head is telling me not to put them in a line like that.
 
Please define what “flat” means to you and acceptable distortion might be.

I would assume he wants it flat within a couple thou since it's a bed for a 3D printer. But the flexible plates they are putting on top of this would need to also be pretty much dead nuts flat and parallel also.
 
Possibly do the ol' automotive trick - build it, heat it up to operating temp, then grind or face mill if that's good enough, at the temp you will be running. In fact, that's a good application for a shaper.

May be warped on cool-down but should be flat at the operating temp.
 
That force is to prevent the print from pulling up the coated spring steel plate when it shrinks upon cooling, that force is only going to be if you were directly pulling up on the entire surface, but sliding it sideways will be far easier than that.

Obviously with a large enough print the cooling and shrinkage would be able to exert an insane amount of force, but part of this project is wanting to print more ABS which shrinks quite a lot, so going for a lot of retention off the bat is the plan.
 
Well, woof, $113 Canadian pesos for the magnets. This is an expensive week for project parts tossing in some bearings I ordered the wrong size of and wanting some more high strength resins.

I'll be sure to let you guys all know how it turns out.
 
Yeah, I'm sure someone else will have a similar idea to this and stumble across the thread. If it ends up being a waste of money, letting them know in a reply would be good. It does seem I'm the first to try and tackle magnet insertion from the bottom end rather than head on.

Might need some goop to help hold the magnets and steel backing in as well, but with the silicone heater behind them some minor shifting won't really be a big deal.
 








 
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