[diyengineer]

Hello! I need 4 parts machined out of MDF, plastic, wood, etc. Something that is 1/2" thick and cheap. I am using these parts as a plug for a aluminum sand casting mold. You could obtain the MDF @ home depots for less then $20 dollars for a monster sheet. (Note: The holes are not to be tapped. Just drilled to there correct size indicated within the documents)

A CNC router, or mill can be used as long as you can hold tight tolerances and are accurate.

2 pictures are below, along with the PDF 2D drawings of each. I have the full solidworks files i can disclose to you if you tell me your email.

I can try and convert into other files as well if it makes it easier for you.
I would like to have this job handed out by the end of this weekend (oct. 3rd), and receive the parts by next week. I can pay VIA paypal.

shoot me an email or PM. [email protected]
Please include pictures of work you have done, the tolerances your machine will hold, or other notable characteristics about yourself. Last time i gave work away to the cheapest bidder i got crap parts. Never again.

Thank you very much, i look forward to getting my machine running with these parts!

[diyengineer]

Need these routed asap Any takers?! DIY'ers!?

[harryn]

Hi, I am not bidding (don't have a cnc yet) but I do have a few observations.

a) It is handy to post what state you are in, because shipping is probably significant for heavy parts.

b) Ability to be built
- I am honestly not sure that these can be built from mdf or low quality materials.
- Deep holes in the flange with only 1/8 in walls
- dimensions targeted to 0.001 inch - not many diy routers can do that, and perhaps not that many industrial routers either. Of course, no problem for a metal mill
- hole drilled / countersunk very close to the edge of a piece

I think the only way you can get a piece made like this would be to use an engineering plastic, such as delrin, or in a foam material, a very high density foam specifically for this kind of machining. I would use Al if there is no other reason not to.

These materials are readily available, just not something you can buy at home depot inexpensively.

I am still learning, so my observations might be way off, that is just what I am imagining from looking at the parts.

[diyengineer]

A. Washington State.
B. -MDF works perfectly, its high density gives amazing results.
-Yes there targeted to .001". I've seen multiple routers on here be that accurate. If they are not no big deal. I've stated in the first "post the tolerances your machine will hold". If you can get close enough say < +- .005 ill be a happy camper.
- The edge distance is fine. I've already made a mock up unit by hand out of MDF and bored those holes with a drill press fine.

C. This is a plug for a CASTING. Why would i have it machined out of aluminum, then turn around and use the aluminum piece in a sand mold that i intend to fill with molten aluminum? Aluminum 1/2" plate is $$$, MDF is not.
If i planned on keeping the plugs for a long time and using them a lot, i would go with a aluminum or plastic like you suggested so that it would not expand/contract as much with humidity, heat, etc. MDF likes to asorb moisture, warp, etc. I'm not going to keep it that long, i just need a plug to cast and go. Once i have the first aluminum copies they will be permanent, and i can use those for plugs in the future if something breaks.
Once i get my machine up and running i can CNC cut my own pieces out to replace the castings if i desire.

I'm not putting a man on the moon, just trying to hold a servo against a rack with a spring.

Thanks for your observations! I hope you get your CNC soon It is addictive!

Hi, I am not bidding (don't have a cnc yet) but I do have a few observations.

a) It is handy to post what state you are in, because shipping is probably significant for heavy parts.

b) Ability to be built
- I am honestly not sure that these can be built from mdf or low quality materials.
- Deep holes in the flange with only 1/8 in walls
- dimensions targeted to 0.001 inch - not many diy routers can do that, and perhaps not that many industrial routers either. Of course, no problem for a metal mill
- hole drilled / countersunk very close to the edge of a piece

I think the only way you can get a piece made like this would be to use an engineering plastic, such as delrin, or in a foam material, a very high density foam specifically for this kind of machining. I would use Al if there is no other reason not to.

These materials are readily available, just not something you can buy at home depot inexpensively.

I am still learning, so my observations might be way off, that is just what I am imagining from looking at the parts.

[Boltz]

Hi, nice drawings!

I'm curious about your casting process... those holes and counterbores don't look like they would sandcast with good definition. Have you cast parts with this level of detail to your satisfaction before? The counterbores might require a secondary, wiping out the cost saving of cast versus plate.

regards,
-Jim Hart

[diyengineer]

Hi, nice drawings!

I'm curious about your casting process... those holes and counterbores don't look like they would sandcast with good definition. Have you cast parts with this level of detail to your satisfaction before? The counterbores might require a secondary, wiping out the cost saving of cast versus plate.

regards,
-Jim Hart

They wont be a problem. If they are i will just tape off the holes, cast the main pieces then located and drill the holes by hand.

The best thing is if anything happens and you screw up, just throw the casting back in the crucible and melt it back down and give it a second try
Ill post pictures of the finished product for everyone to see once i'm done.

If someone milled the pieces out of lost foam,( polystyrene foam ) I could easily cast it in two seconds with the holes and counter bores.

So i guess add foam to your list.

Let me know if anyone can do it.

[acondit]

So, have you calculated shrink into your patterns? Have you allowed for draft so that the patterns can be withdrawn from the sand without spoiling the mold? Have you provided machining allowance for the surfaces that need a machined fit rather than as cast?

Alan

[diyengineer]

So, have you calculated shrink into your patterns? Have you allowed for draft so that the patterns can be withdrawn from the sand without spoiling the mold? Have you provided machining allowance for the surfaces that need a machined fit rather than as cast?

Alan

I don't plan on copying the parts to exactly .001", or i would just have them machined. I don't even need that sort of perfection. I can however make a dang good clone of a machined piece, that would easily work for my application.

I made a working model by hand from MDF already based off of those plans. I printed the plans out, cut them out by hand, taped them onto the wood and cut and sanded them out. They worked perfect. I'm not a master woodworker, but its safe to say that a cnc router is more accurate then my hand. So if my hands can make a piece work, surely a cnc router is more then capable of working.

If i get a good clone then i can cast it no problem. As for the bearing i will probably JB weld it in the cast hole, if the hole is to tight ill use a rotary file and open it up then Jb it in.

Once my machine runs, i will machine my own replacement pieces.

Eventually i would love to get into super precision casting and see what tolerances i could hold, i think it would be fun. For this though, it is not necessary at this point and time. This is just a simple bolt on structure that holds a servo. The servo motor plate is free floating and is held against the gear rack with a 20lb spring.

Worst comes to worst ill remake the new revision by hand and cast it. It would just be nice to get a really accurate cnc cut model to start off with.

Thanks everyone.

[diyengineer]

So, have you calculated shrink into your patterns? Have you allowed for draft so that the patterns can be withdrawn from the sand without spoiling the mold? Have you provided machining allowance for the surfaces that need a machined fit rather than as cast?

Alan

I saw your website! Sweet router and foundry btw!

[diyengineer]

Here is 2 pictures of the 1st mock-up prototype by hand. this was just to see if the concept would work and if i was off on any overall measurements. Designed first in solid works, but all the dimensions were taken by hand with a Starrett steel rule. I used plastic white cylinders and slots instead of a bearing since i didn't have one at the moment. That gave the motor plate a certain degree of controlled movement and act as if it were on a bearing.

Anyways maybe that helps a bit.

[acondit]

I wasn't questioning your design, per se. It is just that Aluminum shrinks about 1/4" per foot, so when you are designing patterns to be cast, you don't just use your final measurements. You have to allow for that shrinkage in your patterns.

In the pattern shop we have special rulers that have the shrink already calculated. If we draw a line 12" long with a 1/4"in 12 shrink ruler, the line will actually measure 12.25" long.

Alan

[diyengineer]

I wasn't questioning your design, per se. It is just that Aluminum shrinks about 1/4" per foot, so when you are designing patterns to be cast, you don't just use your final measurements. You have to allow for that shrinkage in your patterns.

In the pattern shop we have special rulers that have the shrink already calculated. If we draw a line 12" long with a 1/4"in 12 shrink ruler, the line will actually measure 12.25" long.

Alan

Well that shows how much i know! :O
I had no clue it was that great of shrinkage! I assume when you pour its so hot the metal is fully expanded (in terms of volume) into the cavity, and upon cooling to room temperature, it contracts to its final resting place. hmm...

So essentially i would have to account for thermal expansion in EVERYTHING i planned on making. Design the part, then off the part, design a mold that accounts for the expansion.. That will sure be fun! =(
I need to buy a few books on precision sand casting and mold making. I'm sure that would really help me out in future endeavors! Thanks Alan!!

[acondit]

I have my new router almost completed. I just have to finish the cable chain and limit switches on the z-axis. I live in Oregon so if you haven't found someone to help you by the time I finish, I will try to help you out.

Alan

[RotarySMP]

As Alan pointed out, you need to account for shrinkage. Casting patterns also need draft so you can get them out of the mould, also pointed out by Alan. As such a cast part can not have a vertical sides, therefore you can't get parts from these patterns which can be bolted together without further machining.

You can not sand cast small parallel walled holes in parts using a normall pattern (no draft, and no sand strength).

Have you tried running your machine with your MDF patterns installed? You should be able to mill Aluminium sheet with your router using the MDF parts installed temporarily.

The draft issue is avoided if you do investment casting, such as lost foam.

Since these are simple 2D shapes, you could easily make patterns out of 1/2" polystyrene foam sheet with a simple template and a hot wire cutter. This would be be a simple job for an afternoon.

Drill the holes after casting.

[diyengineer]

I think i just have them machined then i can get my cnc running faster. I will have to play around with the castings on the side and see what kind of tolerances i can hold etc. I'm sure i could do it, but it would take some time and i just want to see this machine move haha! I figure i'll go with the collective advice of many smart people then to waste a lot of time and money :P

I will try casting my old mockup unit for the hell of it while the new plates get machined. I found someone to machine the parts as well.

As Alan pointed out, you need to account for shrinkage. Casting patterns also need draft so you can get them out of the mould, also pointed out by Alan. As such a cast part can not have a vertical sides, therefore you can't get parts from these patterns which can be bolted together without further machining.

You can not sand cast small parallel walled holes in parts using a normall pattern (no draft, and no sand strength).

Have you tried running your machine with your MDF patterns installed? You should be able to mill Aluminium sheet with your router using the MDF parts installed temporarily.

The draft issue is avoided if you do investment casting, such as lost foam.

Since these are simple 2D shapes, you could easily make patterns out of 1/2" polystyrene foam sheet with a simple template and a hot wire cutter. This would be be a simple job for an afternoon.

Drill the holes after casting.

[RotarySMP]

If you look at your current design it is optimised for 2D machining from flat stock. reproducing this design 1:1 with castings gains you nothing, as you have all the disadvantages of machined parts, but pick up non of the advantages of castings.

The big advantage of casting is the ease of creating 3D compound shapes. It would be a great learning project to take a look at the part you are trying to make, assembled from the current four parts, and try to design a single casting to replace this assembly.

You have mentioned tolerances and casting often. You are not going to get finished mechanical interface parts out of a sand casting without finish machining. The art of casting is abut identifying what features need no tolerances, and which are tolerance features which will be finished machined, and try to optimise your design such that the casting needs as little machine as possible using as few setups as possible.

[diyengineer]

Ya, im getting it machined from Plate instead
I know its not optimized, i wanna see how far its off with my own 2 eyes. then i can mic and measure exactly how far its off and what the whole thing is doing. I can read about it all day long but i wanna see what will exactly happen, then i can change accordingly in the future.

Your last part is very well stated. I would like to learn how to cast like that, get a shape down where some parts need no tolerances while being able to finish machine certain parts that do.

Thanks everyone for the help!

If you look at your current design it is optimised for 2D machining from flat stock. reproducing this design 1:1 with castings gains you nothing, as you have all the disadvantages of machined parts, but pick up non of the advantages of castings.

The big advantage of casting is the ease of creating 3D compound shapes. It would be a great learning project to take a look at the part you are trying to make, assembled from the current four parts, and try to design a single casting to replace this assembly.

You have mentioned tolerances and casting often. You are not going to get finished mechanical interface parts out of a sand casting without finish machining. The art of casting is abut identifying what features need no tolerances, and which are tolerance features which will be finished machined, and try to optimise your design such that the casting needs as little machine as possible using as few setups as possible.