Cutting MDF with a Spiral Saw Problems

[Skaught]

I'm trying to cut a circle out of 1/2" MDF with a Craftsman spiral/rotary saw. The kind of saw that looks like a Dremel on steroids. Anyway, when I sink the bit into the MDF (goes in fine), but I can't push it a centiemeter. It just sits there spinning until it starts to burn the MDF through friction.

My hope is I just have the wrong bit. Maybe it's a drywall bit and can't cut wood. I dunno. 1/2" MDF isn't that think. My jigsaw makes quick work of it. Has anyone else had a problem with one of these saws? I have a circle cutter attachment that will let me make a perfect circle (as opposed to a jagged thing a jigsaw would provide), so I sure hope I get this working right.

Scott

 

[Node Nine]

I have cut holes in MDF just this way and have not seen this before. I hesitate to ask, but are you sure you are not running in reverse? Maybe the cutter is plunged in past the cutting flutes and is bearing on the shank of the cutter?

EDIT: Since the initial plunge is working, running in reverse would seem to be ruled out. Check your depth of cut.

 

[ReallyCoolStuff]

I prefer to draw the circle with a dark, very fine pen(with a compass), cut it out with a band saw or jigsaw about a 32nd or so outside the line and then use my stationary disk sander to remove the rest up to the line. With a litter practice you develop a "feel" for it and I get extremely accurate circles that way. More so than any other method. Try it!

 

[Hangar18Studios]

It sounds like your bit is dull. Also, cutting MDF at high speeds can not only burn, but clog bits and blades. Can you slow the RPM's down on the tool at all?
I'd buy a new cutting bit. You can also try spraying silicone on the bit, but you'd probably have to do that every inch.
Scott

 

[Rebelscum]

This sounds like you're using the wrong kind of bit. This kind of cut is done all the time with a normal fluted router bit, though I have no idea what kind of bit is in your tool. If it's something like a drill bit, I can't imagine it working in mdf.

 

[Pete SSS]

This sounds like you're using the wrong kind of bit. This kind of cut is done all the time with a normal fluted router bit, though I have no idea what kind of bit is in your tool. If it's something like a drill bit, I can't imagine it working in mdf.

This sounds about right to me too, a nice new router bit should see you through.

 

[CustomCreations]

Are you using a Rotozip then?
I have one, its pretty good and shouldnt have a problem with MDF, although it does cut too fast really.The blades overheat and dull quickly with mdf if you work too fast.
You mention you cant push it, you either have a really dead cutting bit as said, or the bit itself is clamped too low in the machine chuck and you have plunged it deeper than the teeth on the blade, so you are effectively only cutting with half the teeth- the other half is plain metal, so it wont be going anywhere once down into the MDF...hope this makes sense.

 

[Skaught]

Yep, wrong bit. I bought some new ones for wood and that did the trick. Looking at the bits I had, they had a different spiral, so I think those must have been for drywall.

Even with the compass, I still had a couple places where the circle wasn't perfect. Little bumps. I guess I need to practice some. Thankfully, I have to cut out a section and the other section will be hidden, so I can hide the imperfections.

Scott

 

[fuelish]

I have a rotozip and while it is great for rough cutting and boxing out interior holes I have never had much luck being very accurate with it. Even when using a guide it wants to jog around a little.