can't get a square bevel with any sliding miter saw ?

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Forum topic by droppedtuning posted 10-18-2017 10:02 PM 2093 views 0 times favorited 12 replies Add to Favorites Watch
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31 posts in 2851 days

10-18-2017 10:02 PM

i am trying to make some scarf joints on some 8 inch wide boards. no matter what i do i can’t get a square 45 degree bevel. The fence is square ,the blade is fine, it will cut square at 90 and miters are accurate , just will not cut bevels square. I have tried several different brand saws etc. The issue is there is always deflection in the arm when i pull it down to cut the bevel. The saws cut miters fine and cut square except for the bevel situation. Is it just inherent with miter saws? Any wisdom ?

12 replies so far

View cabmaker's profile


1745 posts in 3859 days

#1 posted 10-18-2017 10:37 PM

The only thing i can offer is that i never saw a scarf joint with a bevel.

But…...sliders do inherently exhibit some deflection,,,,especially with dull blades

View runswithscissors's profile


3129 posts in 3076 days

#2 posted 10-18-2017 10:41 PM

Whenever I check out the miter saws (just tire kicking, of course), I always try to see how much flex I can induce in the arm when pulled out for the maximum width of cut. I figure if the saw can cut inaccurately, it willdo so. The more rigid the structure of the saw, the better. The Kapex looks like it might be the best in this regard, but I don’t have one. I do have a Bosch Glide (12”)—used, off CL—and it seems good, but not perfect.

The bigger the blade diameter, the more flex you will get. I think beveling must be the most challenging for a miter saw.

It may be a good, solid RAS, like the older Deltas or Dewalts, might give you the best performance in bevel cutting.

But 45 deg. doesn’t seem like a real scarf joint to me. I guess that’s because in boat work, for example, scarfs typically have anywhere from 1:8 to 1:12 thickness to length ratio. Not something you could do on a miter saw in any case.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View Ripper70's profile


1379 posts in 1959 days

#3 posted 10-18-2017 11:32 PM

Are you clamping the workpiece down? If not, it may help to do so.

What are you using to determine the angle of the bevel? If you’re using the gauge on the saw, are you sure it’s accurately aligned to the saw head? Maybe it needs some fine tuning. An angle finder, like this, is probably the best way to make sure you’re saw is set up properly.

-- "You know, I'm such a great driver, it's incomprehensible that they took my license away." --Vince Ricardo

View Loren's profile (online now)


11136 posts in 4698 days

#4 posted 10-18-2017 11:56 PM

I am assuming you’re pushing the saw head
down to depth prior to starting the cut,
not plunging at the start. That would be
asking for trouble.

I’ve seen claims that the Festool TS75 can make
that cut in 8/4 stock. Another LJ member was
looking for a track saw solution for beveling
slab ends. He seemed convinced the tool would
do it to glue-ready standards.

Google “donkeys ear shooting board” for a
traditional way of refining long end bevels.

View droppedtuning's profile


31 posts in 2851 days

#5 posted 10-19-2017 12:09 AM

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31 posts in 2851 days

#6 posted 10-19-2017 12:26 AM

Maybe scarf joint isn’t the right terminology lol.i am building a 44 foot faux ceiling beam in 4 sections and thought that overlapping 45 degree cuts would hide the joint lines the best

View Aj2's profile


3753 posts in 2848 days

#7 posted 10-19-2017 12:58 AM

Looking at the pic its appears your wood is cupped. All good fitting jointery starts with square flat true reference surfaces. Esp when cutting miters for picture frames. You can still get good 45s you just have to pay attention to how your wood sits against the fence. Or get a better miter saw. That’s my guess from a thousand miles away.

-- Aj

View Jim Jakosh's profile

Jim Jakosh

26056 posts in 4156 days

#8 posted 10-19-2017 01:50 AM

Is the wood truly flat? It looks like there might be a warp across that board which will put some of it further into the blade and make it run out like that.
The other thing that can make that happen is if the wood moves a bit during the cut. Do you have it clamped solid before cutting it?

I take it the wood is laying flat on the bed of the saw and the head is tilted off to the side.

Cheers, Jim

-- Jim Jakosh.....Practical Wood Products...........Learn something new every day!! Variety is the Spice of Life!!

View droppedtuning's profile


31 posts in 2851 days

#9 posted 10-19-2017 02:24 AM

I should have stated the pic is of some scrap used just to illustrate with. My issue is with the saws deflecting to the left since the saw tilts to the left and my bevels are always short closest to me even though 90degree cuts and miters are dead on.i wonder if it’s just a mechanical weakness in sliding miter saws ?

View Lazyman's profile


6925 posts in 2438 days

#10 posted 10-19-2017 12:27 PM

What brand and model of saw are you using?

So are you trying to join the ends of boards? Not sure that a bevel is really going to be that much different than a butt joint at least for hiding the joint anyway. Either way you are going to have a glue joint and wood grain that doesn’t match up between boards not to mention a fairly weak joint. A spline might be a better option as it will help align them and make a stronger joint. Might be a pain to cut on the end of a long board though if you don’t have a router and a slot cutter bit.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View mike02130's profile


170 posts in 1723 days

#11 posted 10-19-2017 03:27 PM

I’ve had the same situation over my thirty year career. I just kick the saw over a half a degree or so to compensate. The use of a scarf joint is really not necessary and actually the wrong way. Wood expands and contracts, thus the long point moves at a different pace and rate than the short point where it meets. Sure, they look nice but after a couple seasons they usually open up. Just use a butt joint with a biscuit.

-- Google first, search forums second, ask questions later.

View Lazyman's profile


6925 posts in 2438 days

#12 posted 10-22-2017 02:05 PM

Another thought…since you are cutting 8” boards I assume your saw a sliding miter saw and not just a “chop” saw? Did you try making a shallow scoring pass before you make cut to depth? This may help reduce the tendency to deflect. You could even take 3 passes and reduce the deflection even more. I suppose the quality, type and condition of the blade could make a difference as well.
(EDIT: Just noticed that Loren basically made the same suggestion.)

But again, I would probably opt for a spline joint rather than the miter joint.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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