Thick section casting (CNC Router Drop Plate)

[HT1]

when you have to do a thick plate, mold manipulation is always the way to go. I will explain. clamp a board to both sides of the mold, botom and top. so it is one unit. after pouring roll the entire mold up on it's side( this must be done quickly so consider placing it on some sort of pivot to make it easy. help is in order for this) the gating system should end up on the top. attach risers to the side of the runner opposite of the gates to feed the casting . even without the risers, you are very likely to end up with the shrinkage in the ingates rather then a hugh "fallen cake " look right in the middle of the plate.

[Harry]

Great tip HT1, thanks. How about pouring vertically? I suppose that means a lot more fall for the metal into the mold cavity though. The other thought I had and have been doing some experimenting with is just propping the mold at a slight angle. I think I will try this piece at about 20* or so.

I think I would have trouble with tipping the flask unless I had a helper or a pivot as you said. A pivot could be pretty simple though with a latch that caught once raised so it could be lifted one handed. Will think on this some.

This also makes me think of what Oldfoundryguy was starting to tell us about on the old forum before he scratched his posts and left. He was talking about his gravity casting where the mold cavity would be connected to a well, the well would be filled by ladle with the correct amount of metal for the part then tilted so that the metal would slide into the mold cavity with very little turbulence.

[HT1]

if you have an option to pour verticle, just use a horn gate so the casting fills from bottm to top. this is the porceedure we used to use for making ring billet for the machine shop. the top will be a little rough, all your dross will be there. but the machine shop would just chuck up the top, and send it back for remelt when they are finished machining whatever part they needed from the billet. but if you are trying to make some sort of flat plate with close dimensional tollerances, mold manipulation is the way to go. pouring verticle causes your draft to make the entire plate look like a wedge. tons of machining to get it flat.

I saw a rig made where the entire mold was placed on a bottom board with a rocker so simply knocking a wedge out of the way, and it would ease right over with just a tap.

over in india, Mold manipulation is HUGH. that is how they make the hollow statues. they actually pour the metal out of the mold after it starts to harden to create a hollow light project. though now days, it is more common to seee two halves welded together. pouring molten metal out of a mold of any type sounds just plain dangerous. and I assume they would be doing that with one of the permanent mold processes vice sand casting

[Peedee]

I've just finished some designs for an injection moulding and through flow analysis I have had to incorporate some 'bow' in the final tool to allow for shrink deformation. I can't show the images and files as it commercialy sensitive but I was wondering if this could be a similar alternative by adding material in the pattern in expectation of the shrink. Plastic injection techniques are remarkably similar to metal casting with shrink bobs gates and runners. Just a thought

[Nudge]

So will the parts be bolted together after it has been cleaned up or will you be casting the final parts like in the last pic? (it is a little hard to see in the photo)

What drivers do you use on your cnc to get 300IPM, I think mine will only do about 300mmPM

[HT1]

I've just finished some designs for an injection moulding and through flow analysis I have had to incorporate some 'bow' in the final tool to allow for shrink deformation. I can't show the images and files as it commercialy sensitive but I was wondering if this could be a similar alternative by adding material in the pattern in expectation of the shrink. Plastic injection techniques are remarkably similar to metal casting with shrink bobs gates and runners. Just a thought

There is a pattern making teqhnique for that, it is EXTREMELY complicated, because you have to calculate the exact shrinkage at individual points in a casting. designing the shrinkage out by using ribs is easier, and saves metal. it is how the professionals do it. look at the bottom of your drill press or bandsaw table top


potentially offensive to some



Us amature casters have a tendency to shortcut on the design & patternmaking, because we are all excited to get to the molten metal, or do not have the proper pattern making tools available to us. probably why in the professional realm, the two jobs are completely seperate. so you see alot of people, myself included trying to work out design problems as casting problems. there is a trade off. I know sanding pieces of 1/16 wood down to size is not my favorite task but sometimes it is the way to go especially if you hope to make hundreds of parts to sell for a profit. but if you just need one for your own use, and are having fun with the heat, try a couple of different casting techniques... well it is a learning experience

[Harry]

Peedee, I am happy to get my parts near net then mill them to finished dimensions. Considering the competition in many of these markets uses 6061 plate their material cost are very high along with waste and material removal which means time. The 6061 t6 is a harder material but if there is room for using thicker sections, engineered ribs as HT1 has mentioned and non rectangular shapes to trim weight without losing strength A356 non treated will fill the bill quite nicely and mean it is a labor (mostly cnc machine time) component that makes up most of the cost rather than material and labor can be translated into personal profit.

Nudge, I used #8 on this page but the next machine I am building will use this setup from cncrouterparts.com with the g540. These setups will move the machine at speeds in excess of 1K IPM for rapids. Cutting is a function of bit, DoC, material and RPM though so to speed up cutting for a particular material it is not only the motor pushing the spindle around but also the spindle itself with some high end spindles approaching 100K RPM if not over. The whole idea is to be able to get the material out of the way fast enough for the bit to move along without over shooting this too much as that would add friction and more heat. Also when milling metal the heat is carried away with the chips when the removal rate and RPM are closely matched.

The complete mount and drop plate in the drawing is three pieces and will be bolted from the back side with three bolts in each of the two mounts. I am also working on some fixtures that will be used for machining these parts I will post on as I progress. The goal is to make setup as quick as possible.

HT1, anyone taking offense to good advice needs to read elsewhere

try a couple of different casting techniques... well it is a learning experience

That is something I do all the time, wasting a mold means a few minutes of my time which would be no different than reading a book (other than the sweat) or a forum like this one but it gives hands on feedback with huge reinforcement as to what works and what doesnt.

[Nudge]

#8 is a 4 axis setup. Do you use the forth axis for turnung on the spindle or have you made your mill with axis.

Have you got an over all pic of your setup. I am thinking of re building my mill soon.
I would love to have one of your setups but I only have the space for a desk top mill. The one I have at the moment will cut an A4 paper size, the entire mill is 16"x 22" with a 8" Z lift.
Do you think it is possible to down size the parts of your setup to make a desk top version? What I was thinking is cut parts on the mill I have to make the new mill. I could be your market supplier for this side of the ditch?

[Harry]

The 4th axis is slaved to the Y since the gantry is powered on both sides so it is Y/A

I am close to having all the parts to build a smaller machine, the current one only gets used in a small area most of the time and by having a smaller foot print it will be much stiffer which will be even better for milling aluminum. I will be using 4' Y and 3' X for a work envelope of 3 x 2' on the new machine.

You could certainly use your current machine for making patterns to make the trucks for a machine. I would be remiss if I did not say it would be money well spent to join Joes forum even if you are not buying a kit from him or I. There is a wealth of information there well worth the cost of entry plus current modifications that have come about in large part from individual builders.

As far as a local supplier, I wish I had enough volume to warrant it. I have sold a few kits in AU but with shipping being around $100 and the limited number at this point it would be tough to work out. You would certainly be on my list though if were to happen.

I will get a thread going soon on the machine along with some pictures, there are a few videos on youtube (castcnc) if you havent seen them.

[dallen]

Harry;
Was wondeering if you had found a solution to your shrinkage problem with this part??, if so how did you eleminate the shrinkage??.