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Accuracy/squareness of sliding miter saw?

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Forum topic by IdahoEv posted 04-12-2016 12:52 PM 967 views 0 times favorited 16 replies Add to Favorites Watch
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IdahoEv

7 posts in 237 days


04-12-2016 12:52 PM

Topic tags/keywords: miter saw question

I just bought my first sliding miter saw. I settled on the Craftsman 10” compact, mostly because it seemed to get good reviews and my bench is only 30” deep so most compound sliding miter saws won’t fit.

Anyway—I’m having trouble getting the thing square enough to produce miters that won’t visibly gap. I’ve spent about four hours trying to square both the fence and the bevel.

I’m not sure if the problem is the saw, or my technique, or if I’m just expecting too much of this tool and this level of inaccuracy is totally normal.

Using a two-cut technique, I can’t get better than about 0.015” accuracy along a 12” crosscut. Because at that point, the tool itself seems to have more error than that from cut to cut. Trying to adjust finer than that doesn’t help much if the tool is flexing by 0.02”+ Is that normal for this sort of saw, or should I be expecting better results than that?

There’s a lot of info online about how to square and measure a miter saw, but not much about how much error one should tolerate.

The attached picture shows three test cuts I made at 90° in a foot-wide piece of MDF (cut, flip, cut). I measured with calipers at both ends. You can see that in the top piece, the left end was wider by 0.020”, but in the bottom one the RIGHT end was wider, by about 0.002”. Is that typical for a saw like this?

Blade used was a 60-tooth craftsman brand, thin kerf. Both it and the saw are brand new.


16 replies so far

View geekwoodworker's profile

geekwoodworker

352 posts in 922 days


#1 posted 04-12-2016 01:02 PM

Those saws are generally made for framing and that is more than accurate enough for rough carpentry. If you want perfect 90 deg cuts for fine furniture then you need to make a cross cut sled for your table saw.

I use my mitre saw only for rough cuts and framing. For which I never use it in the woodshop for making furniture.

View rwe2156's profile

rwe2156

2192 posts in 943 days


#2 posted 04-12-2016 02:33 PM

I settled on the Craftsman 10” compact

I always check the reviews before buying (not the consumer reviews, the industry reviews).

Fine Woodworking had a very good miter saw review a few months ago.
You can download the PDF here. The CM didn’t make the list but I’m sure you can find it reviewed somewhere.

Popular ww’ing as well as LJ are also good places to look.

Its probably the sliding mechanism, but before you take it back, have you put a good blade on it? Most of the time the blade that comes on the machine is inferior. The cheaper made saws like this will have more arbor run out, cheaper bearings and motors.

You’ll never totally rely on it for accurate cuts so I would take it back.

-- Everything is a prototype thats why its one of a kind!!

View waho6o9's profile

waho6o9

7172 posts in 2039 days


#3 posted 04-12-2016 02:36 PM

Get a high quality blade

View bonesbr549's profile

bonesbr549

1176 posts in 2529 days


#4 posted 04-12-2016 02:39 PM

1.5 thou across 12” for a craftsman is pretty dang good. You don’t mention if you are using a good quality blade either thin kerf, deflection?

For true miter I’d go with either a miter sled you make or an incra miter gauge with vernier scale. That allows you to dial in by the thou and it will hold.

I have a capex and its dead on but that was a significant investment.

However even with the kapex, I still when that 45 has to be dead on, I go with the incra. Also with the vernier scale, you can sneak up on the opposite angle. In other words if one side is 45.02, and the opposite is 44.98, its all good.

-- Sooner or later Liberals run out of other people's money.

View Bill White's profile

Bill White

4450 posts in 3423 days


#5 posted 04-12-2016 02:40 PM

Take it back to the “Crapsman” store.
Bill

-- bill@magraphics.us

View IdahoEv's profile

IdahoEv

7 posts in 237 days


#6 posted 04-12-2016 04:45 PM

Thanks everyone for the replies. Will respond to a few comments at once, here.


I always check the reviews before buying (not the consumer reviews, the industry reviews).

I did read a bunch of reviews, of course. I didn’t bookmark them all after reading, but it got good reviews in several places. Here’s one: http://www.woodworkersjournal.com/10-sliding-compound-miter-saws-tested-reviewed/


Its probably the sliding mechanism, but before you take it back, have you put a good blade on it?

It’s hidden at the bottom of my post, but yes I did upgrade the blade. Not to the top of the line, because I wasn’t about to spend a lot of money on blades at sears. I have a Diablo 60 tooth on the way that will be here tomorrow, I’ll test it again then. But given that I can deflect the cutting head about 3/32” when fully extended, using only a few pounds of force, I don’t think the blade is the biggest part of the problem.


1.5 thou across 12” for a craftsman is pretty dang good.

Check the decimal point … more like 15-20 thou, not 1.5. :-) If it was 1.5 I’d be pretty happy.


For true miter I’d go with either a miter sled you make or an incra miter gauge with vernier scale.

If you want perfect 90 deg cuts for fine furniture then you need to make a cross cut sled for your table saw.

Alas that I don’t really have space for a good table saw (and certainly not the budget right now). :-(

View devann's profile

devann

2200 posts in 2155 days


#7 posted 04-12-2016 05:12 PM

Miter saw are made for trim. Radial arm saw are made for framing. You don’t have to believe me, just ask any trim carpenter what he uses. 99% of the use a miter saw, the other 1% uses a table saw and sled.

Has with any tool you get what you pay for.

Easiest way to check and see if your miter saw is cutting true. Take a board, about as long as the base of the saw. Set the saw to 0°/90°. Cut the board in half. Flip one half of the board over and rejoin the cut. If it doesn’t fit back together perfectly your saw is out of adjustment by the amount of gap that you’re looking at.

-- Darrell, making more sawdust than I know what to do with

View TMGStudioFurniture's profile

TMGStudioFurniture

55 posts in 281 days


#8 posted 04-12-2016 08:23 PM

I don’t think miter saws are really meant for high-precision work – the evidence is simply how much flex there is in the whole mechanism, especially when a slider is extended.

One thing that you can try is to reduce the spring tension that rotates the saw upward. This might help you use a lighter touch, and can help minimize the overall flex.

Also, be aware of your technique, in the sense of pushing the saw straight down. You might even try a few test cuts pushing differently, and see how much variation you get.

-- https://www.etsy.com/shop/TMGStudioFurniture

View Bill White's profile

Bill White

4450 posts in 3423 days


#9 posted 04-12-2016 10:12 PM

My DeWalt non-slider is very accurate. I will stand by my earlier post. Take it back.
Bill

-- bill@magraphics.us

View knotscott's profile

knotscott

7210 posts in 2838 days


#10 posted 04-12-2016 11:08 PM

I’d start with a better grade of blade, and would go with a full kerf, not a thin kerf at that diameter. A 12” Craftsman thin kerf blade is a pretty wide span to expect not to flex.

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

View AZWoody's profile

AZWoody

693 posts in 686 days


#11 posted 04-12-2016 11:32 PM



My DeWalt non-slider is very accurate. I will stand by my earlier post. Take it back.
Bill

- Bill White

Any non slider is going to be more accurate than a sliding miter saw.
I have a DeWalt 12” slider that I can not get to cut a perfect 90 degree cut.

I also have the same Craftsman the OP has and it cuts 90 no problem. Sounds like you have a personal issue with anything if it has the Craftsman brand on it. Before I bought it, I checked reviews and it came up as a very well rated saw. Plus, it can be pushed up against a wall and still work, which is the main reason I bought it.

OP, I agree with others the first thing to do is change the blade. I would do full kerf for any miter saw and then from there, you can start to check the mechanics of the saw itself.

View IdahoEv's profile

IdahoEv

7 posts in 237 days


#12 posted 04-18-2016 07:07 PM

Just to close the loop on this thread: I returned the craftsman. After playing with a bunch of other display saws, I determined that its slop really was only a little worse than other sliders (though much less than the Bosch glider, which was pretty rigid). However it did have a significant bow to the fence, with the inner edge of the right fence bowed in by 0.016” (see picture). I checked the display model and it was exactly the same, so I think it’s a casting problem common to the line. That’s certainly enough that right and left miters will never match.

After reading the posts here and doing some other research I decided I would be better suited with a 12” non-sliding miter than any sliding miter, and would save a bunch of $$ to boot. So I returned the craftsman to Sears and bought a Dewalt DW716 non-slider instead. I used it all weekend and was pretty happy with the results.

Thanks so much for the input, everyone.

View TMGStudioFurniture's profile

TMGStudioFurniture

55 posts in 281 days


#13 posted 04-19-2016 06:24 PM

I had a similar problem with my miter saw (not a c-man). You can correct that problem, basically by removing the fence, laying it face down on some spacers, then whacking the back side with a hammer. You just build a ‘bridge’ type of affair, then tap it so it is more true.

Afterwards, you can sand that flatter if you want, just by putting a piece of sandpaper face up on a known flat surface (glass, cast iron, etc.), and taking out the high spots.

I think it’s pretty much the same with all tools – if you want the maximum accuracy you’ll need to figure out how to adjust/achieve that, because most of this stuff doesn’t come set up perfectly from the factory. The tool doesn’t provide high standard work, the operator does.

-- https://www.etsy.com/shop/TMGStudioFurniture

View IdahoEv's profile

IdahoEv

7 posts in 237 days


#14 posted 04-20-2016 05:34 PM



I think it s pretty much the same with all tools – if you want the maximum accuracy you ll need to figure out how to adjust/achieve that, because most of this stuff doesn t come set up perfectly from the factory.

I contemplating making such modifications—but in the end decided it was better to begin with a tool that started in better shape. The Dewalt had an admirably flat and parallel fence right out of the box.

View TMGStudioFurniture's profile

TMGStudioFurniture

55 posts in 281 days


#15 posted 04-20-2016 06:24 PM

So, the real question is: if you perform the same test on the Dewalt as you did on the C-man, are your results improved?

I’m guessing, based on the C-man test, though, that you can’t even compare the two, since you are comparing a slider to a non-slider, and your initial test involved using the slider to its maximum capacity.

I wonder, if you had locked the C-man slider in place, and used it like a non-slider, would you have gotten the same accuracy as the Dewalt? (or at least close enough to be negligible.)

-- https://www.etsy.com/shop/TMGStudioFurniture

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