Material Question

[phd1658]

I need to carve a circular pattern for a foundry. The pattern is 15.5" in diameter and has a z of about .5". The foundry will make a wax casting from it, do some hand detailing, and then make a rubber mold. Here's the question: What material should I use to cut the pattern? It needs to be about .75" thick and at least 16" wide. Any suggestions would be appreciated!

[tgm]

We have done some similar work and the best material we have found is double refined, moulding grade MDF usually available from most suppliers. Machines perfectly with a minimum of fuzz and hold details well. Believe me it's not the same as regular run of the mill MDF.

Good Luck,

Tom in PA

[phd1658]

Thanks, Tom. I know this sounds like a real novice question (for good reason!), but when you say "available from most suppliers", are you taking a Lowes or Home Depot, or a more specialized type supplier? Thanks again!

[gene]

You can get mdf at lowes and home depot but it most likely will not be double refined. This is used for molding and cabinet doors. I would check at a cabinet supplier first . If you cant find it then do the other but it will need some sanding , it sands easily its just time consuming . The double refined is also sold as "door core"

[coach]

I have made 3D parts for a medallion maker. He made rubber molds then poured the parts from concrete.

We always used HDU.

[chiloquinruss]

When I cut patterns for the local foundry I use the Beckwith tapered cutters but I don't use mdf. I always make the patterns out of laminated hardwood (what ever I have on hand) and when completely sanded smooth I give it several coats of shelac with a final wet sand of 400. If you don't use some form of tapered bit the mold won't release properly, at least mine didn't! Russ

http://www.beckwithdecor.com/index_files/Cutters.htm

[phd1658]

Thanks for all the input! I found the double refined MDF at lunch today. I'm using Artcam, which has a draft feature to take care of the mold release issues..........I hope! It looks like I have prospects of an ongoing relationship with this particular foundry, so if any one else has any thoughts or experiences on the subject in general, any additional input is appreciated.

[harold_weber]

If it were me, I would go and ask the foundry what material and draft angle they prefer, after all they are your customer.........................

[kfitz]

Probably does not need to be very precise, but you might want to find out if shrinkage is a factor too.

[navigator7]

Any suggestions would be appreciated!

Bill,
There are two types of foundries. One takes all comers. These are called Jobbing Foundries. The other is a captive foundry, in that they cast for themselves or are into production line casting. Some foundries just produce one or two parts. Like chickens produce eggs. The jobbing foundry that takes all comers is a real talent pool, rare and a dying breed. (At least 20 years ago.)

My guess would be it's captive foundry seeking your skills as they are stuck like much of the nation...with less work than normal and trying to stay alive. They have no need for a pattern maker normally as patterns are most likely machined steel printing part after part into the flask. The pouring part is easy....creating the pattern is the bugaboo.

In the olden days...the Pattern Maker was a gifted and skilled artisan. A shopbot and a guy that can create a file on demand is a dream come true.

Traditionally, the type of wood used depended in the type of material poured, the weight of the pattern and the amount of intended usage.
Color of the pattern told the foundry men what the pour metal should be due to shrinkage of different materials. Yellow red and black where pattern colors I remember for aluminum brass and bronze but I forget what goes to what.

You should find out what type of foundry you are working for. Next, find out if they use match plates.

If they do, you can create match plate patterns that affix directly to their match plates saving them a huge amount of grief.

Sounds like they may be doing a lost wax casting which is probably a bronze job.

I don't know how much puters, cnc and CAD has affected foundries in the last 20 years but it has got to be for the better! It used to be a month's worth of work for a pattern maker to work his magic and then tweak the pattern. What a SB can do in seconds ...a fillet for example, would take a pattern maker a week.

Now....Keerist......A complicated pattern can be done in a day or so.

My suggestion, if you are going to work for these guys, is to learn as much as you can about metal casting and pattern making. Learn the lingo. Terms like risers, runners, gates, sprues, chokes, chills, cores, lost wax and such.
The principles of melting metal does not change despite CAD and puters.

Not only can you create the pattern for the part, you can create the riser, runners and sprues. Not only is the shape of these items important, so is their location....just as important as the pattern!

The Metalcaster's Bible by C.W. Ammen by TAB Books is a book I cannot recommend highly enough.

http://www.amazon.com/Metalcasters-B.../dp/0830699708
Buy a used one if you have to. Buy anything by CW Ammen. Each is a gold mine of information and nearly everything in this book applies to a shopbot owner.
CNC wasn't even around when this book was published but everything a shopbot does is needed when making patterns.

A warning....you might get sucked into the craft. Building fixtures for your bot....ooops, I digress again.....

HTH