How much danger am I in running my circular saw backwards?

Background: I’ve built myself a workbench topped with an 11/16" layer of plywood and 3/4" layer of melamine particle board. I need to trim the edges so that the layers match and are the right distance from the lower boundary of the frame.

The melamine coating is prone to chipping, because circular saws cut upward. I’ve tried various tricks I’ve seen on the web: in particular, putting masking tape on the edge, and doing a shallow (1/8") initial cut. The masking tape was worthless and the shallow cut was ok but still imperfect.

In principle, I could simply take off the top, flip it over, and do the cut that way. It’s tempting, but it’s already screwed securely in place and I feel like if I remove it, it’ll be impossible to get it back and aligned again.

When doing test cuts, I noticed that the bottom edge is absolutely perfect. Not too much of a surprise since the blade is moving in the opposite direction there, plunging into the material instead of pulling out.

I could achieve the same effect by running the saw in the backwards direction (the blade is still going the same way, I’m just moving it in the opposite direction). I realize this has the potential for “ramping” and getting away from me, but this is a wimpy 5.5" battery powered saw. Furthermore, I’m not standing inline with the cut (I’m standing astride the saw in either case).

Is there some risk I’m not considering? Another way to cut that would be more effective? Some other tool I could use (a table saw is out, but a router might be acceptable)?

If you have a clamped-on saw guide, I don’t think this would be too dangerous. You would have to pull the blade guard all the way back at the start of the cut, which is a little risky.
A first-pass with a saw, and then a cleanup pass with a router would also work, and would probably leave a nicer edge.

Terrifying thread title there Dr. Threadside manner could use a little work. Responding to the title and not the actual post, no more dangerous than riding the missile down yelling “Yeehaw”

Part of the reason the blade cuts as it does(when operated normally) is to help prevent bucking and kickback. I suppose if you turned the saw around…no, sorry, having experienced kickback with a toekick saw, the idea is just…no. maybe you can invert the blade on the saw itself?

I’ve done the shallow cut, and it worked well. But the advice I was given, “shallow” was no where near 1/8". I was told to adjust the saw so it just cuts (scores) through the melamine alone.

That worked for me, but maybe I’m not as fussy about melamine edges as you are:)

While I would *never *admit to stooping to clickbait, I must acknowledge that adding a little punch to a title never hurt anyone.

Putting the blade in backwards wouldn’t work–the saw *spins *the same way no matter what, so that would just have the effect of ensuring I can’t actually cut anything (though I suppose it might burn through the wood if pushed hard enough).

I’d never heard of a toekick saw, so I had to look that up. I suppose the difference here is that I do have a nice rip guide here (in the form of some MDF sheet clamped to the table), so I can exert a fair amount of pressure down and against the guide.

In some ways, this is actually a less awkward cutting position, since I’m left-handed and I have a right-handed saw. It switches handedness when changing direction!

**beowulff **is of courseright that I have to deal with the blade guard, but that’s not too big an issue I think. No need to poke at it when the blade is spinning, just move it beforehand.

Interesting–I’ll try that. The advice I saw actually advocated a 1/4" cut, which seemed way too deep. The melamine is super-thin, probably not even 1/32". It might be a bit tricky to adjust my saw to that but I’ll give it a shot.

It doesn’t have to come out perfect–this is a workbench, not a kitchen cabinet–but it would be nice to get it as close as I can. I’ll be adding an iron-on edging strip once I get the edge cut.

I was thinking invert the blade and then pull the saw instead of pushing it. Then it would cut from the top down instead of the bottom up. Still gives me the willies though.

If you do this you are in danger of dying. If you use a circular saw at all you are in danger of dying. I’m not sure how much more danger you will be in from doing this, but it’s certainly more danger than using the saw the proper way.

Score it with a utility knife. Just the melamine at the inside edge of the cut. Then do the shallow cut to get down to wood. Then the full cut.

You can get a harbor freight trim router (small hand-held router designed for what you’re trying to do) for $30 (24 with a coupon) and a decent bit for $10. Using tools in a manner for which they are not designed often lead to "hold my beer"moments. spend the 40 and use the right tool.

A router is the right tool for this job. if you do any significant amount of woodworking, you should have a router anyway.

Ding ding ding, we have a winner. I had the same issue and this worked perfectly.

It’s much safer running the saw backwards, but you still have to take care not to accidentally join things together.

I expect that even a wimpy battery saw has enough power to get away from you if it catches something wrong. I will join the chorus saying don’t do this. Not worth it.

If you reverse the polarity on a microwave you can make ice cubes in 30 seconds.

A laminate trimmer bit in a router would be ideal.

What about clamping a thin piece of masonite on top and cutting through that, so the melamine isn’t the last thing hit by the blade?

^This is a good option.

The technique the OP was asking about is called climb cutting and can be very dangerous because the blade will be pulling the the saw towards you.

You won’t benefit from the risk as the chip out will be happening to the bottom of the sheet.

Update time!

Contrary to best practices, I gave the whole backwards thing a shot. What’s the worst that could happen? My high school shop teacher had at least 8.5 fingers and seemed to do all right. Result:

  • The edge quality still wasn’t that great. Not sure why the bottom edge was perfect before–maybe something to do with the angle of entry for the teeth?
  • My battery-powered saw is in fact wimpy. A couple of times I ran it a little too quick and the saw stopped. No jerk; not even a little jump. The blade just stopped and I had to back off and restart.

Ok, next plan: pre-scoring. This did not go well. Maybe I just suck with a blade but I found it difficult to really make a straight line. The blade, pressed against the guide board, wandered too much: either it would steer into the board and jam, or steer away and leave a wavy line. Some kind of jig would have helped I suppose but I wasn’t in the mood to build one.

Finally: buy a router. This, in fact, was the right solution. Perfect edge quality with zero difficulty. The only difficulty is that the starter set of bits was not long enough, so I have another on order. But aside from that, the edge is perfect, as is the face of the particleboard.

So hey, learning experience. It’s possible that using a sacrificial sheet of masonite, etc. would have worked but I don’t have enough scrap laying around and buying more is an unpleasant experience.

Thanks for the advice, all, even if I didn’t always follow it.

The edges break where the blade is cutting without support of the substrate. going forward the cutting tooth is coming up to cut the melamine which is supported by the substrate. As the tooth exits the sheet the top melamine is not supported in the direction of cut.

Going backwards just does the same thing in reverse while increasing risk to you losing fingers/feet/thigh bones.

Are you using a laminate blade? They will have a much different rake and many more teeth, likely a negative rake unlike wood cutting blade with positive rakes.

the higher number of teeth mean that each tooth bites less, with less risk of chipping and the negative rake reduces the aggression of the tooth as well.