Pricing help on bronze plaque

[cnc_works]

I'm being asked to bid a bronze plaque (1/8" thick), something like 48" X 48", about a third 1/2" text and maybe a quarter of it 3" high text. 3D engraving on serifed text, obviously the large text will have to be depth limited.

My clear problems are: Keeping the bronze flat enough to get uniform engraving, cutting bronze in general, and, last but not least, pricing.

I'm thinking of vacuum to hold it flat or clamping cauls across it and doing a section at a time.

Pricing, I just dunno, wild guess is something in the $1200 range. More if I have to put together a temp vacuum plenum.

The other thing that's scary is the responsibility of delivering a no mistakes job on satin metal with no imperfections allowed.

So, any suggestions, pointing out anything I'm not thinking about would be very welcome.

PRT96, PC890 router, by the way. (Spindle arriving this week I hope...oh boy!)

Donn

[rick_woodward]

First thing that jumps out at me is the high probablility of "eating" this job,time and materials.Everyones idea of "perfect" is different.Second is the satin finish. This may require buffing equipment/tools and or glass bead blasting. Or some other media.I dont work with metals but even in wood there are tooling marks every where.... 4" x 4' wow. smoothing out tooling marks around all the letters. To perfection. Hope your bed is perfectly flat.Others with metal/bronze experience in what your looking at , hopefully will join in with their knowledge and experience.Wouldnt even think of this without a spindle. Just my thoughts.

[rookie432]

My first thought is to mill this in another material then use sculpt nuveau bronze on it. Heck, you could mill a few and give them the best one as perfect. At least you would have more controll over the finish and it would be a real metal finish that could be buffed. I can't tell the difference between real bronze and the sculpt nuvea product in many cases.

2 cents
Bill

[joe]

I'd consider the Bronze surface material by "Sculpt Nouveau".

Pricing is easy. Look at the price a foundry would charge. Check with Gemini. www.signletters.com (http://www.signletters.com)
J

[tim_whitcher]

A cast bronze plaque would be between $3000.00 and $4000.00, but would obviously be a completely different animal.

[cnc_works]

I appreciate all the responses. I did describe the Art Nouveau process to them, but as I expected, the architect's specs won. I plan to apply Gerber Mask II to both protect the surface and make painting (to be done by the client) easier.

I've cut a sample and had it approved by my client. I'm going to bid about double what my limited experience dictates would be a "no problem" job, (total $1875) then cross my fingers.

A follow-up question. I engraved the 7/16" letters with a 45deg v bit. I wonder if 60deg would give me clearer serifs?

For info, I engraved the sample at about 20K, .1 ips, two passes: one at .04" and one at full depth. I have since replaced my PC with a spindle, I suspect I'll probably drop the rpms and leave the feed speed the same. As usual, any comments appreciated.

Donn

[joe]

Donn,

How did that project turn out?

[cnc_works]

Hey Joe!

Well, I did the test with my router and they weren't really satisfied, as mentioned I just installed a spindle and that took enough of the chatter out of the edges of the letters that they accepted my bid of $2300 for the whole job. I had no idea how much play there was in router bearings until I did the side by side. They're serious, already got half.

I'm going to have them cover the whole blank with Gerber Mask II to protect it and to provide masking for the painting to be done by someone else.

My main worry is flatness of the bronze plaque, so I expect to flatten my table, then use curved clamping cauls to hold the plaque flat, doing only a few lines at a time between the cauls.

Next worry is a programming glitch so I'll run a test cut in 1/4" melamine at a slightly increased feed speed.

Still wondering about a 45deg vs a 60deg v bit for the smaller letters (about 1/2" high). Also wondering about any more suggestions as to feeds and speeds with a spindle in bronze.

Hope to get the whole thing going next week. I'll post results when I'm done. An obit if things don't go so well.

Donn

[rookie432]

Hey Don,

I'd kindof be interested in seeing that side by side of router cut verses spindle cut if you don't mind. Just curious as to how much chatter a spindle really reduices.

Thanks
Bill

[cnc_works]

Bill, I'll try to get pix of the test blank on the forum soon. I must say, no doubt I did a lot of quality work with the router, but I'm in love with the spindle. The smooth, quiet power, ahhhhhhhhhhh! Going back to the router would be as hard as going back to dial-up from broadband.

I'm so sold that I'm going to get a 1hp spindle for my smaller cnc.

Donn

[joe]

Donn,

We're rooouting for you. Keep us informed. I'd like to try one of these but I'm too chicken. Also I have the Gemini catalogue.

Joe

[cbradshaw]

Donn,

I sold a brass plaque 48 x 24 that I bought for approx. $1100 and sold for $1900. All I had to do was order the sign, drill four holes in a brick wall and mount it. The ordering and installation took about 2 hours total and i didn't have to worry about mis-machining it. This was the easiest $800 I have ever made.

Carroll

[joe]

Me too Carroll,

That's www.signletters.com (http://www.signletters.com) Their plaque's come in so many textures and shades. I think the prices are very reasonable and down right high quality too. If you ge their catalogue, and let them know you are selling signs, there is a 40% discount.

J.

[cnc_works]

An update to this bronze project.

I ended up making a dedicated vacuum table to hold the bronze flat, which was the major problem in engraving the plaque. The small v-engraved letters required a flatness less than plus or minus .003" to achieve uniform cuts. It was an absolute bear to get close to this tolerance but, for the most part I was able to do it. I wasn't happy in the spots where the tolerance was exceeded, but my customer was tickled, so I guess that is all that matters.

One normal 2 flute V cutter cut the whole plaque at 10-20ipm, about 16K on the spindle. If I slowed down the spindle it began to burr, so despite the recommendations of Onsrud on slower cut RPM, I increased rpm until I got no burring, little chatter. I used Gerber Mask II, cut it dry, could not even use air cooling because it loosened the edges of the mask.

I don't think that I would ever take on a job again, but just because of the challenge of keeping it flat. Maybe 2' X 3' would be max for me.

I thought I was bidding the job extravagantly, but in the end, I do believe I earned every penny, if not in hours, in fingernail biting tension, especially when I pulled the trigger for the first cut.

Thanks for the help and suggestions.

Donn

[jhicks]

Donn, with that behind you, do you thinik it would make any sense to carve a mold, and have it poured by a sand cast foundry?
I've discussed this with a local Aluminum casting foundry and it sounds pretty basic and economical but don't know about Bronze. Just sounds like it may be the way to go for future signs or letters.
Any thoughts on this approach out there?

[cnc_works]

Jerry, my customer considered it and, though I don't know it directly, I understood they found that process to be considerably more expensive than my bid, in the realm of double.

Donn