Cutting mdf arches

[loriny]

Can anyone point me in the right direction? I do custom arches. usually have ripped wood, bent and glued and then run through my woodmaster(with custom knife). I hoped to learn machine more before having to put to the test. I have a customer looking for 2 paint grade MDF arches in a basic profile- something like a brick mould, he said-. I have a prt 96 w Geckos, A probe and vector aspire.
Where should I start? oh yeah- he wants the arches in a week.
any help would be relly appreciated

[loriny]

I found some info in the archives. I will probably probe the elipse and either scan a drawing or probe the profile. Then to figure how to sweep it to the elipse. Any tricks?

[porscheman]

Lorin,

I've been designing and cutting some molding profiles, both straight and curved, using Aspire's two-rail sweep functionality. The rails you need for this approach will come from probing the ellipse or template for your arch (the second rail is simply offset from the first by the width of the profile). The shape of the profile comes from your probed profile result, or by just approximating it using curved and straight vector segments.

Check the Aspire documentation and tutorials for more information on two-rail sweeps. Hope this info helps.

John

[zeykr]

I may be misunderstanding what you are trying to do, but why wouldn't you draw and then cut on the shopbot the Mdf Arch, then run it through the woodmaster to create the profile just like you do with the bent wood arches?

[loriny]

mostly to see if I can do it. also by the time I get the carbide knife ordered and delivered I would be to my deadline.

[blackhawk]

Lorin - I did the same thing as you are trying except that I was making the profile on straight pieces. My wife wanted a picture frame and I didn't want to buy knives for my Woodmaster either. I just drew two straight lines for my rails. I then went to the Woodmaster website and I just picked one of their picture frame patterns on the website. I copied the picture of the profile and imported it into Aspire. I then edited it a little and did the two rail sweep just like John suggests. It worked great. Just make your rails curved as you need them and it should work.

[bill.young]

There's also a Virtual Tool in the ShopBot software called the "Extruder" that may do what you want, depending on the shape of your arch. You can access it in the "Tools" menu and read about how it works by clicking the Help icon button once it's open.

Bill

[jhicks]

I have made many custom arches in MDF and solids and find the most effective way is a knife for the profile and the bot for the arch blank. Given you are only cutting 2 I wouldnt spend on a carbide since the steel will certainly make it thru two arches and can be expedited with Woodmaster.
The time and detailing you will need to go thru to machine an extruded design could definately work but the best bang for the buck in the knife.

[fishhawk]

Jerry, I agree with your direction. My question is if you are cutting the arch blanks out of MDF or hardwood, what joint would you use that would hold up to the stress of the woodmaster blade?

Matt

[jhicks]

Matt, I've done both MDF and Solids in Poplar Mahogany, and Oak plus a few more exotics like bloodwood. For MDF, its a no brainer, nest arches in the sheet, give yourself an additional tail on each leg maybe 6" longer than the finished piece needed to account for the final miter joint and a bit of twisting as it feeds into the curved arch table fixture on the initial feed as it alligns to the radius fixture and fence.
Also you can experience some planer snipe on the exit end.
To reduce snipe on both ends, feed the arch into the table and keep upward pressure on the other end as it feeds into the 1st roller until the leading end gets through the knife and under the second roller.
On the outfeed side, same thing. Lift the arch as it exits the table slightly to make sure the trailing end doesn't lift inside the planer when the 1st roller releases as it is exiting in the final 6" or so.
On solids, all I do is miter the solid on appropriate angle to provide for the needed arch and over cut. Butt joined and glued with clamps to join and dry.
Then mount the blank with screws to a spoil board, cut your arch, and profile just like any other material.
A butt joint is a lot of surface area and holds well plus you get a nice grain direction in the arch toward the center peak rather than the laminated layer look.
If you try to use a finger joint or tounge and groove, it won't look too good over the cut of the profile when you're done. You'll get a wavy zig zag depending on the profile shape and depth.
Butt joint is a nice clean line as grains mismatch at the miter but they can get pretty close if you're joining the same piece of stock.
I think I had a few photos on my web site but its the most efficient way found.
I usually feed stock on the 18" planer with a 5HP motor and a single knife at about 40% max feed rate but the woodmaster guys can help with feed rate for your machine and species.
Slower is usually better to keep knife chatter down with more cuts per inch fed.
If you need anything, just drop me a note or call.
Keep the prices up there. Arches generate good margins and most dont have this capability so they labor over laminating a long time with lots of clamps and time spent and yours will look better when you're done.
The other think I like to suggest is a center medallion or pendant. That way you dont join anything. Just buy wide enough stock for 1/2" the arch and make 2 pieces with the decorative center. Sell it for more and work less at it.
Go get em!

[loriny]

Do you always run on a spoil board? If you do are you using a setup like the WH machines to guide it with rollers or do you use the guides that woodmaster recommends?
I have been bending and laminating thinking this was best but I will have to try the Butt joints now that I have cnc, and see how it looks.

[wberminio]

Jerry

What type of adhesive do you use to butt joint your
pieces?

Erminio

[loriny]

I have gotten the 2 sweeps done but I can't figure out how to get them past this point. The only tool path I can create is the one to cut out the outside vectors. I have the 2 nested on a 4x8 sheet of mdf and could cut them free it looks like. However I would like to cut the profile (good practice) and it is very simple, just a small bead with a v groove on the inside. I am able to see the profile on the 3D view but don't know what to do from here. I might be missing something but I don't see the info I need in the instructions or tutorials.

[loriny]

I got pointed in the right direction on the vectric forum. I am close to figuring it out now

[jhicks]

Ermino, believe it or not, good old tight bond exterior works just fine.
Lorin, I do use a spoil board to cut the shape on the bot and simply screw the blank down in areas outside the shape. Often I'll add the drill holes to the cut file, drill shallow holes for positioning in the blank 1st, then screw it down. Then I know I wont be hitting any screws.
I use the woodmaster radius table/bed fixture for feeding the blank through the planer/profiling the knife cut.
I think you'll appreciate both the time savings and the results compared to the laminated / bending methods