How would you make this disc.

[Roger Haar]

Hi,

About once a year I make about 200 disc out of MDF. These disc are

3.25 inch in diameter, 1/2" thick with an axial 3/8" hole. The rim of the disc has a groove 1/4" deep and 1/4' wide around the circumference so that from the side a cross-section looks like:

__ __ | | | | | |__| | | | | | | | | | | | | | | | | | | | | __ | | | | | |_| |_|

I cut the MDF into squares and then gang cut these squares into octagons. Up to this point things go fast. Next,I mount about a dozen octagons at a time on a threaded rod which is held in a metal turning lathe by a three jaw chuck and a live center in the tailstock. Things do no have to be very precise so I can eyeball the side-to-side position of the groove and use a stop to control the depth. My cutter is the width of the groove. I have colored paper between the octagons so that I can more easily see where to cut the groove.

Is there some easier way to do this? Molded solid platic probably could work, but the cost for a small run might be high, I have thought of using a hole saw and cut two thin (0.125") discs 3.25" diameter with a hole saw and a 2.75 diameter disc that is 0.25 thick. But my experience with hole saws usually involve lots of fighting to get the disc free.

Any ideas? Thanks

Roger Haar

[Tim Wescott]

If it works for you to assemble them and glue -- what about having your blanks laser cut, and gluing them together using a 3/8" mandrel? This will go a lot quicker for you, and having 600 pieces cut should spread out the laser cutter's set-up and programming costs nicely.

[jwdoylejr]

Think about a router with table. Groove cutters for routers are available in sizes to suit your need.

The router table should come equipped with a miter fence, like a table saw. You could mount a vertical pin on the miter slide bar to act as a pivot for the drilled octagon blanks. Mount a blank on the pin, shove it in to a stop, and rotate it with a suitable pusher -- keep fingers out. A small plumber's helper would do for a pusher. Once set up, you should be able to turn out two or three disks per minute.

Side benefit. This is a very good excuse to buy that router you've always wanted.

Pat

[whit3rd]

Easiest way to make disks is with a hole saw; your axial hole is a tad bigger than the pilot drills, so the hole and groove will probably need separate operations. Carbide-tip and high quality holesaws have proper tooth set and the disks will come cleanly free. Unlike square-then-cut processes, you will be able to cut disks in a hexagonal array (less waste) and might be able to get more from a sheet.

I'd think of a lathe faceplate with a centering pin, perhaps just clamped with a live center; it'd be quick to unclamp and go to the next workpiece.

And if you can do it, grind a long 3/8" drill's tip to make a pilot that matches the holesaw's pilot, then the drill-out of the center is just a matter of handheld drilling in a drill press,

[brianlanning]

They wouldn't get stuck in this:

you could gang them together, a stack of the smaller inner disk, then a stack of the larger outer disk. You wouldn't have to adhere the layers together either. If you started with 4"x4" squares, you could use that shape to line them up on the DP against a fence and stop.

If the drill hole in the middle is 1/4 instead of 3/8, it would be easy to mount a jig on the drill press to line up the disks exactly to drill the holes out to 3/8.

Glue them up on the threaded rod in stacks. Mayme make wooden pieces for the ends to distribute pressure, then crank down some nuts on the threaded rod to act as clamps. The only problem I see with this is squeeze-out polluting the 1/4" grooves. If you're careful, you could probably eliminate that. Or you could use high-tack spray adhesive to bond the three disks together.

brian

Roger Haar wrote:

[Tom Gardner]

How long does it take to do them now?

[SonomaProducts.com]

Use a circle cutter which will leave a center hole for the axle too.

on the router table get a slot cutting bit. Make a jig that fits in the table slot and has a pin for holding the circle center. Setup a stop on the table so you slide the jig forward until the slot cutter is to the depth you want, then spin the circle.

Be careful to keep the circle from spinning out of control and wear a mask if useing MDF.

Roger Haar wrote:

[Bob May]

I've got one of those cutters and it works very well for making round things out of stock. I've even done 3/4" stock with no problems. Make sure that you hold the material down firmly as the drill bit can walk about and enlarge the hole even tho it is a special cut with no side cutting tooth.

-- Yeppie, Bush is such an idiot that He usually outwits everybody else. How dumb!

[Gary Brady]

I'd use a router and a circle cutting jig, sort of like a trammel point. One operation for the intitial cutout, and another for the groove on the edge. The circle cutting jig makes an exact circle but there's no possiblility of gang cutting.

[steamer]

--Just out of curiosity what's the application??

--What he said, but I'd suggest using vacuum fixtures to hold each part in place on a series of stages, each equipped with a template so that the parts could be routed in steps, so you'd only have to change bits once for each batch. I've done production work with routers and fixtures and this is a reeeally fast method for multiple parts. As you move down the line towards finished part you can make use of the evolving part shape to design fixtures to hold it in different ways.

[stans4]

I've had a couple of projects like this where I've cut two larger disks and a smaller, then glued them together. If you've got a rigid drill press or mill, General makes sort of a flycutter gizmo for trepanning out circles, the local True Value and Ace stores have them. I replace the center drill bit with a length of rod so the hole doesn't get wallowed out. .25" MDF would be fast to cut, you might want to make a bit ground out of some better stuff than the supplied cutter is made of, good enough for wood, but not for abrasive stuff. The flycutter gives you better control over diameter than a hole saw would and the disks are easy to remove.

Stan

[Roger Shoaf]

I think I would start by cutting strips of the MDF 3 3/8 wide X 48 long.

Next, I would draw a center line down the middle of the strip and walk of center points with a set of dividers every 3.4 inches.

Set up your drill press with a fence and drill your blanks with the circle cutter others have mentioned.

One thing others have not suggested is using a router bit with a bearing on it to control the depth of the cut. This is a whole lot easier than rigging a fence.

The slot can also be done on the lathe, easiest would be a metal lathe with a mandrel set up, but the router would be the quickest way.

Last step would be to enlarge the 1/4" hole to 3/8". To do this I would make a jig by screwing a piece of 1/4" or 3/8" to a sheet of 1/2" or 3/4" and adjust your circle cutter so that the hole you make has an inside diameter of 3 1/4 so your parts fit snug. With this clamped on your drill press you should be able to drill out the pilot hole to size with no problem.

I would recommend either a forstner bit or a brad point bit and to prevent tearout, you might want to punch it half way and flip the disk over.

What are you using all of these disks for anyway?

[Leuf]

I think the way you're doing it is pretty effective. Instead of cutting off the corners you might be better off ganging them into a shorter stack and cutting them slightly oversize with a circle cutting jig on the bandsaw.

To speed up the cutting of the grooves you could make a notched jig for the tool rest that would control the position and depth of cut. You could also make a "forked" cutter that would do two grooves at once.

I can't see cutting them one at a time on a router table being faster.

-Leuf

[todd1814]

B&D Jigsaw, sharpened screwdriver and a beer bottle.

Figure that out...