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://g-ecx.images-amazon.com/images/G/01/ciu/24/b6/840b228348a0311ea04fe010.L.jpg
http://www.amazon.com/Metalcasters-Bible-C-W-Ammen/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

[garyb]

Thanks for the plug Russ

Bill, even though you can add draft in ArtCam it's a lot quicker toolpath and machine time to use a tapered cutter if you can get away with it, 1, 3, 5 and 7 degrees are your standards for 1/8 ballnose, 3, 5 and 7 for 1/4" ballnose.

[phd1658]

Thanks again, all. Chuck, this guy is a jobber. definitely old school. The work he has produced is absolutely beautiful and definitely high end. I will buy the Ammen book. Besides, it is too late, I am already sucked in! Except for a four year stretch in the Army, I have been involved in some form of manufacture all my life and have always been fascinated with its various forms. Besides, it has occurred to me that should I sell production pieces, it would sure save time to do some cold casting with the metalized paint versus carving everything every time.

Gary, or anybody, if you have artcam and use a tapered ball nose, how do you "define" it in Artcam? Do you just tell it the diameter at the nose and not enter anything about the angle or do you try and define it as if it were a V bit?

Thanks again,

Bill

[garyb]

Bill, to set up a tapered ball nose in ArtCam you can create a new tool and select the radius engraving from the tool type drop down.

Myself, if I want a small draft angle and am relying on the cutter to get it then I will tell the software I'm using a straight ballnose but use the tapered and machine to my selected vectors.

[bryson]

Sorry I missed this one. I second everything that Chuck has said. I operate my own cast aluminum foundry which is why I purchased my bot. I can add one more thing to the material list. I have also used Corian for my casting patterns. It cuts easily and doesn't need any sealing. I have just started a project for number plaques that incorporates using street names that I can change quite easily. The street names and numbers are held in with bees wax.
Bryson

[phd1658]

Wow, nice work, Bryson! Thanks for the tip on the Corian. I just got some in to play with lithopanes, but it is too thin. I'll have to try some. I'm guessing I could find/buy a suitable piece of Corian (closer to the actual size I need) than buying a whole sheet of double refined MDF. I'm wondering if I can't find anything thick enough..........can you glue Corian up to achieve the needed thickness? If so, what kind of glue would you use? Gary, thanks for the tip on the tool definition.

[bryson]

Bill, I use west System for gluing Corian. I assume that any epoxy would work but I'm a creature of habit and I've been using it for everything since it was called Gougeons!
Bryson

[navigator7]

I operate my own cast aluminum foundry which is why I purchased my bot.
Bryson
Great website, Bryson!
I gotta ask.....
How do you configure your molds when pouring aluminum plaques?
Do you tip the flask?
Do you pour into individual flasks or do you stack flasks and do a multiple mold pour?
What do you find is your minimum thickness for pouring 12" plaques?
Where do you put your riser?
I've got a fire hall logo to pour. They want it in bronze but have a n/a beer budget.
They want a finished look that is very thin...but I want a thicker pattern.
I think it'll produce a misrun or cold shut.

You can respond privately if this post is off the topic?

Tks

Nav7

[bryson]

Chuck, There is a lot of " it depends" there. I've cast as thin as 1/16 in that size range with no problem. You'll need your pour as hot as possible and your sand as dry as possible. I have tipped but I usually gate from both ends and a few vents to keep things moving. I would put the riser opposite the sprue. I added pictures of a 30" X 1 /4" oval that I did. The picture shows the 2 sided imprint in the cope and drag. (This is a home made hinged flask) and gated from one side with a few 1/8" vents.
Bryson

[phd1658]

Bryson, I'll second Chuck's comment on your website, very nice. I'm still working on mine, but it isn't on par. Who did yours? Also, on your corian pieces it appears you put some sort of epoxy in for filler and then sanded? Just curious as to what type epoxy (if that's the case) you're using.

[bryson]

Bill, What you are seeing is melted bees wax. Where you see the street name is pocketed out and I can change them by heating the wax. The numbers just sit on the pattern and they are attached with wax also. The web site was built with Joomla and a lot of tutoring! Check out Weebly, I've been playing with that and it's super easy.
Bryson

[phd1658]

Ahhhhhh, the lightbulb just went off! Guess I need to adjust my thought processes. I asked my wife to order the Ammen book Chuck referred to earlier in the thread. I'll definitely check out Weebly.

[navigator7]

Ahhhhhh, the lightbulb just went off! Guess I need to adjust my thought processes.

Yes you do! Turn that light back on! ;-)
What specifically did you realize?

The "light" that hits me is.....
Before CNC was available to the average man, casting small signs and such was out of the price range of most. Now, the price range for such work is so low.....it is easy to loose your shirt doing one-off's.
You'll have a whole bunch of learning curves:
The Bot
Cad
Flasks
Patterns
The sand, the sand and the sand
The Heat
Finding good aluminum
Cutting off sprues and risers

It's all fun...except the money making part.

[phd1658]

Well, just looking at the picture from the website, I was thinking that Bryson's Corian offerings were simply V carved Corian with epoxy fill....I wasn't thinking about the casting aspects of his work. I have been "working" at working with my foundry contact for some time. A couple of weeks ago, he suggested we "join forces". Not sure exactly what he has in mind, but I intend to find out. I'm a good bit younger than him (if you want to consider 58 "young") and have been looking for some time for something to do once I "retire". Actually, I have no intention of ever retiring, I just want to be able to be creative and work for myself once I call it quits at my present job. The truth of the matter is that it will be awhile before I can economically justify doing so.

It dawned on me very early that Shopbots are very good at a lot of things, but if your getting into relief carvings (2.5D) the time involved is prohibitive if you're planning on any production, and that to make molds, cast the pieces and then pocket out a place for them in wood would be the way to go. My foundry contact has even gone so far as to offer to teach me as much as I care to learn.....I have a relief of a building I had James Booth do for me that I think I could incorporate into sales of a few hundred a year, So I'm thinking that maybe what I should do is carve the building (in reverse) out of corian, with a draft (from earlier comments it sounds like using a tapered bit will be faster than using Artcam's draft feature), and try cold casting it. I'm sure with my foundry contacts help and with the help of the good folks on the forum, it shouldn't take too many trys!

[navigator7]

So I'm thinking that maybe what I should do is carve the building (in reverse) out of corian,...
Gotcha....
Your contacts in the foundry biz are using you to do the exact same thing.
Any file you create in the puter can be a positive or negative.
Hugely useful for creating parting lines and an unbelievable times savings.

If your jobber doesn't have access to this technology currently....his offer to join forces is positive for both of you!

You might consider taking a renewed look at how you save files. I like to save components, assemblies and 'Save-As' rather than 'Save'.

Months to years down the road you get a request for that "thingy" and it can save tons of work.

Regardless.....your prospects sound cool and exciting. I wish you every success!