Making race car body mold plugs

[dauntless]

We are considering purchasing a Shopbot to bring better quality to the patterns we use to make molds for race car bodies, and I have a couple of questions. First, can we start with a router?

Here is a photo of one of our car bodies. The design work is done in Solidworks; then station templates are cut on a 60" CNC plotter/printer, then foam is glued on and rasped/sanded to shape, etc.

http://www.dauntlessracing.com/img/models/P2006.DSR/5_sm.jpg

No matter how much labor we put into the pieces there is always residual waviness, and today's customers expect, well...CNC quality. Hence, we are looking to step up.

Anyway, back to my original question. Can I get started with a router for making MDF pattern pieces up to about 7' long and 2'-3' wide? Or is that not a practical goal without a spindle. I looked for this basic router-versus-spindle question on Shopbot's website, but missed it if it is there.

Thanks in advance!

Stan

PS - and I obviously have not broken the code on how to link to images

[bleeth]

A router inherently has more runout than a spindle. That being said, for station cutting in mdf like that you should be ok with a router.

Although I have never done car bodies I have done many boat plugs and the secret to eliminating waves is always in the final fairing.

For our final fairing material For FRP/Gelcoated plugs we would use duratec high build primer and make up our own fairing boards. For large flat areas they were sometimes as much as 8 feet long. For more highly curved areas we would make them out of thin ply or even bending board to conform to the curve.

For custom hulls that were cold molded wood Fairing was done with West Epoxy mixed with micro baloons.

By the way-Cool way to earn a living!!

[paco]

quote:No matter how much labor we put into the pieces there is always residual waviness, and today's customers expect, well...CNC quality. Hence, we are looking to step up.Can you show us what you mean (pictures).

quote:Anyway, back to my original question. Can I get started with a router for making MDF pattern pieces up to about 7' long and 2'-3' wide? Or is that not a practical goal without a spindle.Routing such molds is 3D machining hence a lots of hours of machining time. A spindle is better suited for long run process. A router is very likely to require maintenance every now and then. I'm thinking you might find more tooling option with the spindle as well...

quote:I looked for this basic router-versus-spindle question on Shopbot's website, but missed it if it is there. Here it is. (http://www.shopbottools.com/FAQproducts.htm#router_or_spindle)

[beacon14]

There may not be a need to make pattern pieces - you can cut the foam directly on the Shopbot.

And yes, you can get started with a router - just get a box of earplugs. When you are ready you can upgrade to a spindle.

[dauntless]

Thanks guys...I really appreciate the feedback. Sorry I didn't post again yesterday, but I ended up spending the day fitting a new engine cover at at a customer's shop and didn't get home until the evening.

Dave, we also use fairing boards, and have no problems in curved areas. It is the long flat sections where it can be noticeable. Perhaps making our flat fairing boards longer would help, so thanks for the tip! BTW, we also use the duratec primer.

Paco, I will try to get photos, but it is a subtle effect. I can see it best in diffuse light at a shallow viewing angle. As one can see in the photo I link to above, the pieces are pretty fair, and the flaws are difficult to see on a painted surface, but in clear coated carbon fiber it can be noticable. And thanks for the link, Paco...I knew that was so basic a question that Shopbot's website just HAD to address it, but I missed it.

David, perhaps I was not clear. We want to change from foam patterns to wood patterns to cut down on the finishing time getting them ready to pull molds from. Customers don't like paying for custom molds, so anything we can do to speed up that process will pay big dividends to us.

Also, we don't do repetitive production work, or not much of it, so maximizing our through-put is not critical. What we DO want to do is to be able to go directly from Solidworks models to positive patterns to molds to finished pieces with minimal hand labor. Right now our biggest single cost area is mold building, where amortizing their cost is difficult when not impossible... ;-)

Thanks again for the input guys!

Stan

[dauntless]

David, perhaps I misread your post. Are you suggesting cutting the molds themselves directly in foam, skipping the pattern step? Thanks! Stan

[beacon14]

What exactly is your process now? It sounds like you are making (or wanting to make) wood patterns that you then use to shape the foam by hand. Foam is much easier to cut than wood. The Shopbot doesn't care whether it's cutting foam, wood, or pickled herring, as long as you can hold it down and create a toolpath for it.

Not sure what bit you would use for pickled herring though.

[dauntless]

Mmmm...pickled herring!


Our present process is to hand shape a full-scale plug in foam. When the shape is complete the foam is finished with glass and body filler, then primed and sanded to 2000 grit and polished to glass smooth. Molds are then pulled from this plug. Hand shaping and finishing the foam is very time and labor intensive, so we are looking to eliminate some of that time by switching to CNC plug shaping, working directly from our Solidworks files. By using MDF in place of foam, we eliminate the time consuming glass-n-body-filler steps and can go straight to primer. We still have the pattern, of course, but much of the most time consuming steps are eliminated.

I have been thinking about trying to use the Shopbot to go directly from Solidworks models to female molds, but need to give it more consideration.

[Brady Watson]

Stan,
I would stick to making a male plug out of MDF & then spray it with Duratec or similar. Using a female plug, it is difficult to get a consistent thickness on the primer, and sags/runs are more prevalent. Bear in mind that you'll want a thick 'tooling' gelcoat on the plug, so you'll have to 3D offset the entire plug to the inside to compensate for this. (which I am sure you already know)

You can cut your plugs with a regular Porter Cable router - but the long milling times & amount of power needed to cut MDF really puts a strain on a router...It isn't really made to do production work...So you may need to factor in bearing changes and things like that in leiu of a spindle.

-B

PS - I've laser scanned NASCAR-type models that were destined to become full scale.

PSS - I've used Duratec as a tooling gelcoat & it holds up REALLY well. I've pulled 50+ parts (airdams) from a set of polyester molds that I refinished with Duratec & they still look/work great.

[gene]

Stan,
I know that theese are not cars but look at this site and you will see some of the things carved in foam foamcarver.com

[dauntless]

Thanks Brady. We already make our patterns about 40-thou under to account for the finish. No harm reminding me, though! We are not looking for high production speed, as we are not making signs or cabinetry, so I am hoping a router will work for a while. Congrats, BTW...I would LOVE to sell 50 of anything!

Thanks Gene...that site has plenty of inspiration, doesn't it?

[hespj]

Stan, I've done a few things like this on the ShopBot (with a router sometimes). This for instance:

http://www.talkshopbot.com/forum/messages/17997/26617.html?1199393452

Some points I'd raise are:

Watch out for those tall vertical surfaces, there's only a certain vertical clearance available before the router hits the workpiece. This depends on the slope of the surface, the width of the router and the length and diameter of the router bit.

MDF is HEAVY.

I suggest you'll need 12" Z (at least) ShopBot to carve such deep shapes. I manage to machine as deep as 8" on a 12" Z machine. That sometimes means making the item in layers and joing the layers together.

The item in the link above wasn't anywhere near as good a finish as you're looking for, and as I say, they took a month. Large areas of 3D are time consuming if a good finish is required. Quicker than doing it by hand though :-)

And (perhaps) stating the obvious - You need to be able to produce a 3D CAD drawing of the item you want to cut, and you then need to produce 3D toolpaths for the ShopBot. Neither is straightforward and both have steep learning curves, but I did it, so you can.

John

[kc10flteng]

Stan...can you get onto Travis AFB...?

[dauntless]

Ron, yes...I am a retired C-5 driver/tactics guy. Ring a bell?

[kc10flteng]

Yeah...thought it was you. Jambo! I've been operating a Prt Alpha 48 x 96/5hp Colombo for 3 years. Cruise by the base wood shop...I'm there.

[dauntless]

Hujambo Ron! My phone number is on the contact page of my website. Give me a shout...and yes, I will swing by the wood shop. Stan

[jackal]

Hi guys,
I'm very new here and I'm pretty much a novice. I do not know anything about shopbot. I have however started building my own supercar project from scratch.......I'mpretty far with it using two part poly urethane which I fill in between chipboard ribs...yeah I know marine ply should of been used. But damn pricy. I have started using a Murcielago as start off for dimensions but I'm shaping it as to be one of a kind. My problem I had was the fact that I needed like a plaster or kind of filler to finish the car off and to be able to sand to smooth. I see you guys talk about fibre glassing the mold and sanding and filling that as to get a smooth finish. I think I will do that. The project car will have hopefully a ausi box and Audi 4.2 liter V8 engine (thinking of RS4)

Chassis will be basically a Lambo chassis (Diablo based)

Thanks for an informative forum.

Cheers
Jackal

[cabnet636]

Spindle and foam!!

jim

7127

[bcondon]

Power Longboard -
http://www.rutuonline.com/html/long_boards.html

This entire site is very interesting and I have talked to Glenn about ihis project..

[terryd]

Jackal, we have done several "supercar" type projects over the last few years including a K1 Attack knockoff. Great work using mdf for us, but an absolute money pit for the inspired. If inspiration and cash exceed fear procede directly to Brady's post above......just save enough for cab fare home

[jackal]

Hi thanx Terry,

Yeah mate, us poor South Africans with our dwindling Rand (about R11 = $1. Yeah it is a difficult situation.a bit of a catch 22. I'm trying to save where I can on the plug manufacturing but I know that the chasis, engine, gearbox electrics and electronics etc.etc. will cost me a fortune anyway! And of course what is the point if it comes out as a Hummer instead of as a Supercar....Sorry for the ignorance, but what is mdf? And is Duratec just a normal fibre glass gelcoat?

Kind regards
Jackal

[terryd]

mdf stands for medium density fiberboard. Most of us over here really think the stuff really is merde but it has its place and building plugs is one use in which it excels. Starting to put clay out of business now that most design and prototyping these days uses 3d software. Duratec is a polyester surfacer primer that is very easy to use compared to gel coat and as Brady pointed out can give you short run molds at a low price and high quality.

[dauntless]

Jackal,

I no longer use mdf to make patterns, and have switched to EPS foam, as it is much lighter and easier to move around, and is quick to cut and easy on tooling. My latest iteration is to do a half-millimeter finishing undercut, then coat with epoxy and about 8 coats of primer, then recut at zero undercut.

You can see some of my work on our website: www.dauntlessracing.com (http://www.dauntlessracing.com).

Best regards,

Stan

[nathanc]

Hi
I'm new here to this forum, but interested in the K1 Attack knockoff that Terry Doherty mentioned. I'm in the process of doing my own chassis and would love to get hold of some Attack based bodywork as a good starting point. If anybody could point me in the right direction, either here in the UK or the US it would be much appreciated.
Thanks
Nathan.
+44 07855 450199

[trackVW]

We are considering purchasing a Shopbot to bring better quality to the patterns we use to make molds for race car bodies, and I have a couple of questions.


Hi......

I was wondering how this worked out for full size race cat bodies ?

I have a project I would like to do and think it might be best to do it in Foam and then fiberglass over it,

thanks for the info

VW