Need to cut a lot of big circles. How would you do this?
Greetings! I appreciate the opportunity to get some ideas on a task I’ve got in front of me.
I need to cut 8.5″ dia circles out of the center of 12″ x 12″ MDF panels. The MDF is 3/4″ thick.
I need to do about 100 of these, so I’m interested in finding a fairly efficient procedure. This doesn’t need to be cabinet grade work (a little tear out won’t hurt anything), but it does need to be accurate.
The end result is the “frame” left behind in the 12″ x 12″ piece. The “wheels” will be scrap.
Idea #1 is to make a simple circle cutter jig for my router and have at it. No reason that won’t work, but I’m guessing it would take forever, particularly since I’d need at least two passes.
Idea #2 is to use one of the large circle cutters in a drill press. The kind with an arm with an adjustable cutter on it. I’ve never used those, and would consider it if I thought the holes would go relatively quickly. I worry that it would be really slow going, though.
And that’s all the ideas I’ve got. Any thoughts on either of those? Any other ideas I’m not thinking of?
Thanks!
Replies
CNC ?
Option 3 make an oversized template using a circle cutting jig for your router then use an appropriate sized router template guide and a new carbide upspiral bit, probably ⅜"d. to maximize strength while reducing load, with a big enough router (2¼hp+) you should be able to hog it all out in one pass.
Forget the drill press circle cutting jigs in mdf they would be almost dangerous with a circle that size.
Either way take precautions against dust. MDF is nasty stuff to breathe in and there will be a lot of dust.
It would be a simple matter to make a clamping jig to align the template with the work piece, assuming the template is 12" x 12" to make a minimal fuss setup. A couple of pieces of 1¼"h pieces of wood attache to a base at right angles would give you a quick reference point and a quick action clamp to hold everything in place. Some 120 grit sandpaper in the center inside the router path would help stabilize the center disk as it gets cut away.
If you have access to a band saw you can make a simple circle cutter with a board and an indexing pin. If not,, if you have a disk sander you can rough out the circles with a jigsaw and use a similar jig to true up the circles.
I think 8+" is pretty large for a wing cutter.
Given that you need 100 of them, I would start thinking differently. Try to find a technique that will let you cut 3 or 4 at a time. Some way to cut a very rough circle, a long flush trim bit, a template and a lot of turners tape. Possibly?
I second the use of a respirator. MDF is hard on the lungs.
I echo what esch said. Big circle cutters are crap, especially on MDF. Use the router in a fixed template, rather than fixing the router to a center pin.
But for 100, finding a shop with a CNC might actually be cheaper.
Router table with a center pin. Doublestick tape on a couple of strips across the top to keep it together as you break through.
First up re-think the task.
Using a solid carbide upcut spiral bit like the #35202 one from Freud in a 2-1/2 hp router. It's cutting length is 2" so you could cut 2 circles per setup. Result: you only need to route 50 circles, not 100. A single bit should stay sharp for 223 feet of cutting, but buy 2 bits in case you break one. Don't be tempted to purchase a low cost bit.
Use hot melt glue to glue the centre 6" x 6" of your MDF squares together.
Use a 1-1/4" high frame, mounted on a spoil board, 2 sets of folding wedges so you can locate the 12" squares in the same orientation each time. Quick clamps will likely get in the way of the router and trammel. Attach a sheet of 100 grit paper to the centre of the spoil board. to grip the bottom disk and stop is sliding around as you break through.
as others have advised, MDF dust is to be avoided like the plague. Wear proper PPE and if possible use a proper HEPA filter dust extractor. Make sure the MDF dust is settled before removing your PPE.
If you share your shop, CAPTURE the MDF dust at source.
Anybody think a Rotozip (they have center pin attachments) might work easier than a router? Very thin cutting tool so could possibly do it in one pass? Never had much use for one for anything else.
Owning a rotozip tool I would say definitely not they are incredibly slow when cutting through anything other than drywall.
Since the OP is interested in making 12" x 12" squares with holes not disks I still feel my suggestion to use a MDF template with a 5/8c O.D. Router guide template and a 3/8" up spiral router bit offers several advantages.
Quick set up if you take a few minutes to construct a simple jig to align the work piece and template.
The work piece is protected from inadvertent damage. A center pin based circle cutter can occasionally jump out and let the router cut beyond the intended limits, thus making the work piece useless. With a template guide the router can never cut beyond the intended diameter meaning you will never destroy a work piece.
Fast production assuming the MDF blocks are precut I would estimate about a 5 min production time for each piece or about 12 /hr. I can't see any other method including CNC being quicker than this.
A large 3hp or larger router should be able to cut this easily in one pass.
You must be referring to a bench top CNC, à larger CNC would take less than 30 seconds.
And it would be dust in someone else's shop. Making 100 of anything from MDF is well worth paying a few bucks for someone else to do. I've sworn off the crap.
I confess to not having any first hand experience with CNCs, but are you factoring in the time it takes to load the workpiece and remove it and load the next?
Thanks for all the ideas, everyone.
Went ahead and built a circle jig for the router. Ran a few and that seems like it's going to work. Still quite a chore (and I drug my workbench out onto the driveway because of all the dust), but it will get there.
Best regards,
In our case, with roughly 30 inches of cuting and a feed rate of 300 inches per minute, it will take 15 seconds for the router to get in position, drill and rout and move away so one can remove the finished part and put a blank so 30 seconds would include handling.
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