relatively cheap CNC services?

Wise and well connected GRM community-

I am trying to find a source for CNC services for a one off prototype of the part pictured below. It's a timing inspection cover for Datsun L series engines, and yes, I do have a license to reproduce the BRE logo.

[IMG]http://i655.photobucket.com/albums/uu276/dimedozen/BREplate01.jpg[/IMG]

The photo shows an earlier version of the design, laser cut in wood by a former co-worker. The specs are as follows: 1/4 thick T5 aluminum, cut on a 3 axis mill, Black anodized finish, the milled portions are .070 deep.

EmachineShop's price for a run of 50 or more of the plates is very reasonable, but for 1 piece they want $469.08, with a 45 business day turnaround time I'm not looking for free, just something slightly more reasonable

Anyone have any lower cost suggestions? I'm open to getting an "unfinished" piece and having it anodized locally.

Thanks, Jeff W.

The Practical Machinist website has a manufacturing resource forum where people post what they want done.

http://www.practicalmachinist.com/vb/forumdisplay.php?f=34

Often there will be 'small time' guys wanting such work.

I'm assuming you have at least a drawing.

Disclaimer: These guys usually don't want to mess with people who aren't willing to pay fairly for their services. Also, don't use the word 'Billet' over there.

-James

Here's the image

check with college's..

at my old school the kids in the shop would run that crap for fun....

especially those on a Baja or FSAE team

Thanks for correcting the image code- should have proofread better. Thanks also for the suggestions, I'll give them a shot. Yes, the drawing exists as an AutoCAD file.

I'll also be sure to avoid using the "B" word- these pieces were originally going to be cast, but unless several hundred or thousand are made, it appears that having them machined will be far cheaper than having tooling made to have them cast.

Jeff

The problem with a lot of little things like this is the set up time is the same for one or a million. Also, it's not an easy thing to get a small aluminum plate for something that size. Well, it's easy to get the plate, just not easy to get it for a decent price. Particularly if you want to spec the temper.

I work at a custom design and fab studio called 3 Axis Inc., we have a CNC router and have cut aluminum and brass with it. There are a couple things with router cutting that will differ from the laser cut wood. Interior corners will be rounded over a little. If a 1/8" bit is used (the smallest we use on metal), then you have a 1/16" radius in your corner. The edges also have a bit of faceted ridge to them. Kind of like on a quarter, but not as grooved. It sands off pretty easily.

I know that we have a bit of 1/4" aluminum scrap around. If you need one, or a handful, we might be able to cut them. If you want the edges finished, and what not, it will cost more, but it's still reasonable.

Actually, a flat part like that, you can cast it yourself. The hard part (the pattern) is already done. Guys in Africa and India and China have been been doing grassroots casting for hundreds of years.

DIY baby!

You can look on the internet for casting advice, or get one of Dave Gingery's books.

Disclaimer: I'm just describing how this can be done, proceed at your own risk.

But here it is in a nutshell. Do this outside in a place where an open charcoal fire and spilled molten aluminum is no big deal. (An aluminum BBQ grill IS NOT cool, it will melt)

Do I have to say BE F&^%$#G CAREFUL!!

1) Get the material (old pistons work well) 2) Throughly mix some fine sand (about 1 gallon) with just enough dino motor oil that it will barely hold together as a clump when you squeeze a handful in your fist. The mixture should be rather dry looking. 3) Make the sand mold by tamping the pattern in face down, and the sand around it, to fully compact the sand around the pattern. Carefully pull it out to leave the impression. 4) Use a leaf blower to supercharge a pile of burning charcoal briquettes 5) Use a stainless pot big enough to hold the metal, and melt the aluminum on the fire. A handle, or vicegrips helps to 6) CAREFULLY skim the dross off the molten aluminum with a long handled steel spoon or ladle. 7) Slowly pour it into the mold.

Let me repeat, BE F&^%$#G CAREFUL!!

Of course, the SO may not be happy with what you've done to her pots'n'pans.

After cooling, you will have to make the rough backside smooth; either have a machine shop mill it, or use a sanding belt to knock it down, followed by rubbing on a sheet of sandpaper layed down on a smooth surface to finish it. You can paint or PC the front, and then finish the raised front part using the sandpaper method.

Of course, if you get ambitious, or want to do a bunch of them, you could look into doing it as an investment casting (lost wax). But that's another post.

Carter

Oh yeah, BTW, eye protection, welding gloves, fire extinguisher, good shoes, etc.you know, all that safety stuff.

Carter

If casting seemed like an option, but the mold is whats throwing you off...

Lost foam casting seems like it would be pretty good. Buy a chunk of foam, carve it out... do some quick reading on designing runners/gating systems/risers and its pretty damn easy. If you can come up with the molten metal its not too hard to come out with a good part.

I understand the reasons for the setup costs for a CNC piece- as BAMF said, shops' costs for setup are the same regardless of the number of pieces run, the larger the number of pieces run, the thinner those costs can be spread. Also, I can only imagine the number of shops that have been burned by people requesting a "prototype", promising to buy a large run, and then dropping off the face of the planet. However, seeing them applied to one piece was very eye-opening.

The advantage to laser cutting patterns is that they require a relatively small amount of cleanup, as the laser beam slightly bevels the material being cut, and with multiple passes, the laser cuts the required draft angle into the pattern.

The backyard casting idea is intriguing, for the experience if nothing else. Not to go off on a tangent, but I've read elsewhere that pistons can be a bad choice for a casting material, depending on the alloy they are cast from. Would older, more cheaply produced (cough: British) pistons be a good choice? I have a box of competition-destroyed stock pistons from a veriety of BMC products that seem like they would be a good choice to melt down due to their relatively small mass.

Tooling also seems that it may be a viable option at this point, I'll have to look into the various methods. Thanks to everyone for getting me pointed in the right direction.

After reading this thread, I'm now trying to think of pieces I need to cast.

That sounds like fun!

Old British pistons (Hepolites, AE's, whatever!) would probably work fine. Old lawn chair frames, window frames, bell housings, master cylinders, whatever you got. But the cleaner the better, less crud to skim off. Stir throughly for a good consistent mixture.

Carter

I'm going to go home and dig out all the pistons I've thrown into my scrap pile.

Im getting all kinds of ideas. Think of all the times you said "this tool works, but if there was a bend here, or it was shaped like this...". Also, accessory pieces or old badges could be easily recreated. The possibilities are endless.

Im off to the boneyard to start grabbing old cracked alloy heads. Now where is that leaf blower I never use...

I see an all new line of eVilallianceracing emblems being produced.

Damn, One more thing, if you are recycling gearbox cases and whatnot to melt, beware of magnesium. Magnesium is neat stuff, it burns with a white, hot flame that's really, really hard to extinguish.

That's one reason they use it to make flares.

If it's mixed in with your aluminum scrap, and you try to melt it, it could explode and burn, and keep burning.

DON'T MESS WITH IT!!

Nuff said?

Carter

erohslc wrote: Damn, One more thing, if you are recycling gearbox cases and whatnot to melt, beware of magnesium. Magnesium is neat stuff, it burns with a white, hot flame that's really, really hard to extinguish.

From my metalcasting book- if you have scrap of questionable makeup, apply a drop of 1% silver nitrate solution to a clean spot on the surface. If you get an instant black stain, it's magnesium. Otherwise, it's aluminum. Having said that, the smallest quantity of 1% silver nitrate I could find offered online was 500ml for $169.XX. Still, it sounds safer than "Aw, hell, throw it in the pot, we're probably fine!"

One more question- i understand that the "back" surface of a casting will require sanding/cleanup, but is it possible to avoid creating a "miniscus" of aluminum to sand off?

What about a water jet cutter? They seem to be very easy to setup based on what I have seen on American Chopper.

I do know VW cases have magnesium in them, that's why Bugs burned so well! Of historical note, the Japanese used a lot of magnesium in the manufacture of the Zero, one of the reasons they burned so violently (non self-sealing gas tanks didn't help of course).

I am not sure "hard" to put out quite describes a magnesium fire!

aircooled wrote: I am not sure "hard" to put out quite describes a magnesium fire!

more like nearly impossible.

I got a friend in CT who has a Haas 3 axis mill and cnc lathe in his garage. ...

If you want I could ask to see if he would be interested in turning out a part or two...

You can avoid the meniscus by going to a full two piece mold, but then you have to have the flask boxes to hold the sand in each piece, you have to add risers, flues, sprues, etc. And then those have to be cut off once the part is cast, and machined, etc. Or go with investmemt casting. Make a mold of the pattern in plaster or urethane, then pour the casting wax into the mold, remove the wax, trim it, then coat the wax with investment, cure it, melt out the wax, pour in the metal, break loose the investment, and finish the part.

Carter