Cutting square planks with a circular saw: doable?

[Ptron]

I made this contraption, which I thought would make it easy to crank out clean, true, right angle plank cuts with just a circular saw.


Note: those blown out screw holes are from my first two attempts at securing the guide board and not getting it perfectly square.

Seemed like a good idea but the cuts aren’t turning out as true as I’d like. They’re pretty close, overall 90 degrees, but just wobbly enough to bug me. Everything glides along smoothly when I cut. It seems like it should be working quite nicely…but then I end up with this.

The guide board looks pretty damn true against a straight edge. I don’t know if it’s not as true as it looks, or it’s the play in my cheap circular saw, or if I’m just not as steady as I think am. Any ideas on how to improve this situation?

You could talk me into getting a good circular saw. That's something I actually use. I’m starting to consider forking out for a table saw but my experience is cheap ones are a pain to use and a good one seems like an extravagant expenditure for how much I’ll use it.

[Le Basseur]

You don't need another saw...your existing one might do a better work if you'd replace your cutting disk with another having more teeth.
I encountered the same problem when I build three pairs of Hedlund horns (alot of cutting,alot of small pieces wich were hard to be put together if not cut precisely.)
If you'd replace the disk,it doesn't have to be from the same brand as others make some more quality products.Just pay attention to the outer diameter,the hole diameter and the overall thickness of the cutting blade:they should be the same as the original.Also,if you have a regular saw disk,you'd might want to try a better one having Vidia teeth.
One more important factor,as I discovered myself:if you have to cut a piece of,say,MDF 18 mm thickness,you HAVE to calibrate the cutting depth on 21 mm (this is the total depth of the cutting disk as measured between the machine base plate and the tip of the lowest tooth). The "3 mm-difference" rule of thumb works great as every mm.counts in this aspect because a steeper teeth angle leads to material chipping.
HTH!
Regards,

P.S.
Please,forget the table saw.
I'm sure that when you work,you pay the utmost attention...but I saw too many people with missing fingers on their hands.

[tubeswell]

If your edges aren't straight, its because you aren't cutting them straight, and that could be your blade, your saw, your jig, the bench it's sitting on, your technique, level of skill, natural tool-handling ability, your wavering limbs etc etc. A joiner will have all the proper equipment and can do a master job in a fraction of the time. Probably less cost overall.

[Ptron]

Thanks folks. I hear ya Tubeswell, but I'm not quite ready to give up yet. I should emphasize that while my results so far are not as perfect as I'd like, they're workable. I could (if I wasn't so OCD) leave well enough alone and move on with the project. The deformations are exaggerated in my drawings. They're really more smooth and sweeping, and only maybe 1/4mm peak to valley.

I noticed that my two test pieces have a very similar curvature to the cut so I'm leaning toward the guide board not being as true is it looks. Or I could have consistent bad motion tendencies as I'm cutting. I'm going to try to find something more precise to use as a guide and see where that gets me.

My blade in is carbide tipped and in pretty good shape yet. I thought it was a crosscut blade but looking at others online, I'm not completely sure it isn't a ripper. It looks to have a pretty aggressive angle on the teeth. You can't read it anymore. I'll have to look into that more.

[nico.verduin]

I take the easy approach....I get the planks I want (from a different supplier) and have it cut to size how I want it. Piss 'm off to cut straight And pay them about 4-5 euros for all the planks of one amp.....

[John_H]

It's probably a combination of things that are causing your poor results. Your saw looks like part of the problem. Cheap direct drive circular saws such as yours are generally not very good. The tables aren't very stable, and don't align with the blade very well. That will allow the blade to wander for sure. If you couple that with an improper, or dull blade it'll never cut straight. A nice worm drive type saw with a new blade will improve your results drastically. I regularly cut hardwood doors with my saw using a cutting guide. With a fresh blade it'll go through 1 3/4" maple, or walnut easily. The Skilsaw MAG77 is what I prefer, and use. Milwaukee, and Bosch make nice saws. Stay away from the Makita.

[Ampclutz]

The not square edge view means your saw isn't adjusted properly. Mess around with the adjustments until it cuts better. They are usually a screw and a lock nut.

You may get better results with a quicker feed of the saw. A smooth consistent flow of the saw can keep the blade from wobbling around sometimes. If your saw is not up to the task abandon all hope and get a better saw...

HTH

AC

[Ptron]

Got a better blade today for starters. It's a 40 tooth finishing blade. Menards didn't have any dedicated crosscut blades. I was using a 24 tooth all-purpose(I think) blade.

I also bought an aluminum guide rail thingy. It's two 51" pieces that can be connected together and used as a guide to rip 4x8 sheets. I'll use one piece for the guide on my contraption and the other for making the baffles. It cost 15 bucks which is more than half what the rest of the jig cost, but still pretty cheap if it works. It occured to me after I bought it that an inexpensive 2' level would also probably work well for a guide rail.

Didn't get a chance to try it tonight, hopefully tomorrow. If I'm still not happy with the results I'll consider a new saw. I've kinda wanted one for a while anyway. Thanks for the heads up on the saw types John.

I haven't checked the exchange rate recently, Nico, but man that seems cheap just for wood, let alone precision cut. What kind of wood are you using?

[sportster4eva]

It's probably a combination of things that are causing your poor results. Your saw looks like part of the problem. Cheap direct drive circular saws such as yours are generally not very good. The tables aren't very stable, and don't align with the blade very well. That will allow the blade to wander for sure. If you couple that with an improper, or dull blade it'll never cut straight. A nice worm drive type saw with a new blade will improve your results drastically. I regularly cut hardwood doors with my saw using a cutting guide. With a fresh blade it'll go through 1 3/4" maple, or walnut easily. The Skilsaw MAG77 is what I prefer, and use. Milwaukee, and Bosch make nice saws. Stay away from the Makita.

Add Craftsman to the stay away list too. It's not a worm drive, which is probably why, but mine has at least a 16th of an inch end play on the blades shaft, and it does the same thing you describe, whether cutting with a guide or freehand. It's ok for chopping off 2 by 4's, but not much else.

[Ptron]

Mine's either a Craftsman or a Black & Decker I don't remember right now. It's certainly got a good deal of play in it whatever it is.

When I was at Menards to buy the new blade, I went down the line of circular saws and checked the play in them. Half were as bad as mine, and half didn't have any play. Strangely, it didn't seem to correlate to how expensive they were (they don't have any really high end ones). I remember the Bosch and Makita ones being bad in particular, while a couple of the cheapies were pretty solid. I wasn't paying attention to whether they were direct/worm drive. There were some of each.

[Ptron]

I tried the new blade first, before replacing the guide fence board, and I got a lot better results. Not perfect, but probably good enough.

I put on the aluminum guide fence hoping that would be the last step to perfection but it didn't make a significant difference. So what little imperfection remains is either due to the play in my saw or the play in me. And since I refuse to take the blame, I'll say it's the saw. Seriously though, I've been trying very hard to make quick smooth cuts. I think with the play in the saw the blade can kind of find it's own way.

Like I said it's good enough, but since I can't leave good enough alone I'm going to try one more thing. Cutting with the router. I don't see why this wouldn't work: using the same jig, and a router with a straight bit? All my 1/4" straight bits are only 3/4" long so I'd have to use my 1/2" by 1" bit. Either that or drop another $15 on a 1/4 x 1 to save a mere inch or 2 of wood. This cheap rig is getting more expensive all the time.

[Ptron]

The router method works pretty dang well, except it doesn't exactly slice through a board like butter. Even with a new, decent quality bit I really had to push it through. I wonder if those spiral cutter bits are better at this sort of thing? Makes a really pretty and smooth edge though.

I'm going to try a two pass technique. Cut the boards an 1/8" long and clean up the cuts with the router. A little extra work but I think the results will be nice.

[Ptron]

Just got back to this project tonight after a little hiatus. The two pass technique works great. I cut the planks an extra 1/8" long with the circular saw, then finished the edges with the router in the same jig. Not only are the edges almost perfectly straight but as an added bonus, the surface texture comes out smoooth. Now it's time to see if the finger joint jig works.

[John_H]

I use a router, and straightedge for joining laminate countertops. Nothing else will give you a cut that clean. When you're cutting wood, be careful to not let the bit get too hot.

[petemoore]

Cut the boards an 1/8" long and clean up the cuts with the router.
Router works great for speaker cutouts, Hacking through as it makes way for the blade is no time to try to get the best finish results, that's for sure, one thing about routers with nice newe blades is the blade can't be blamed for moving around, assuming the bearings are tight.
Maybe a longer, flat sided guide plate.
Firm pressure helps the guide plate push the debris, which can easily throw off squareness. Small amount of take on the finish cut reduces debris.