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Am I expecting too much of this saw?

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Forum topic by Bantam posted 06-13-2019 11:19 PM 544 views 0 times favorited 12 replies Add to Favorites Watch
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Bantam

6 posts in 132 days


06-13-2019 11:19 PM

Hi,
I have a Bosch GCM10SD mitre saw which I bought originally to help building my deck. It was great for cutting the sub frame (9”x3”) and even better with the deck boards, I was very impressed with it. However I am moving in to more precise work now – starting with making boxes so tested the saw for squareness and was disappointed to find it was off by about 0.5 degrees over a 6” wide board. Started with adjusting the fence controlling cutting square across the table and have got this so that the error is reduced to about 0.3 degrees or roughly 0.015” across a 6” oak test board.

Finally the question. Am I expecting too much of this saw? Whilst the blade seems to cut OK it is unchanged wsine it chopped it was though all of the deck lumber so would a new one help. Any advise would be much appreciated.


12 replies so far

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ArtMann

1435 posts in 1329 days


#1 posted 06-14-2019 02:05 PM

I have the 12 inch version of that saw and I have observed the same thing, though not as much as you are seeing. It isn’t really possible to get a tool of this design to cut as accurately as a table saw sled. I attribute the problem to blade vibration. The further from the fence you move the carriage, the more the blade vibrates from side to side. In effect, the saw kerf gets wider. There is no way to adjust that out. For my purposes, that doesn’t matter that much. I think the situation could be improved by using a negative hook angle blade made for a SCMS.

View rbrjr1's profile

rbrjr1

208 posts in 718 days


#2 posted 06-14-2019 02:08 PM

I dont think you are asking too much from a miter saw. You might be asking too much from that particular model, but my Dewalt 12” sliding compound miter saw has been used to cut 5”X5”X5” Regular Pyramids and they came out perfect the first time using the angular detents.

-- only an idiot dismisses an intelligent statement because they dont know anything about the person delivering it.

View Underdog's profile

Underdog

1403 posts in 2548 days


#3 posted 06-14-2019 02:47 PM



I dont think you are asking too much from a miter saw. You might be asking too much from that particular model, but my Dewalt 12” sliding compound miter saw has been used to cut 5”X5”X5” Regular Pyramids and they came out perfect the first time using the angular detents.

- rbrjr1

What blade are you using with your Dewalt?
My DeWalt doesn’t even cut a straight line, so I figure it’s the blade flexing…

-- Jim, Georgia, USA

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rbrjr1

208 posts in 718 days


#4 posted 06-14-2019 02:52 PM

What blade are you using with your Dewalt?
My DeWalt doesn t even cut a straight line, so I figure it s the blade flexing…

- Underdog


I have no idea. a Freud of some sort. it’s not the blade, rip out the owners manual and make the necessary adjustments to the saw to bring it back to square with the fence..

-- only an idiot dismisses an intelligent statement because they dont know anything about the person delivering it.

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Bantam

6 posts in 132 days


#5 posted 06-14-2019 07:29 PM

Hi. Thanks for the advice guys, I was kind of thinking that dead square every time was too much with this saw. The blade I’m using is the original manufactures (Bosch) item so its probably not great. I take the point about blade vibration/flexing at large extensions so here perhaps a new, sharp blade may help – i’ll give that a try.
I was going to build a cross cut sled for my table saw anyway, so I just need to move that up the job list!

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Holbs

2246 posts in 2542 days


#6 posted 06-15-2019 12:56 AM

I have learned you can not expect 0.001” perfection in miter saw cuts, as it’s not their purpose.
However, techniques come to mind to help.
I now slowly engage the wood piece, giving enough time for the saw blade gullets to clear out debris. This has help immensely to give a more accurate cut. Slamming down a cut with a miter saw will always give you saw blade deflection.
And of course, fine tuning everything and realizing you will have to fine tune once again later on as things eventually move.
I too used the default Bosch miter saw blade. Migrated to the Forrest Chop saw blade (which seems to be of thicker metal/less deflection) and the teeth do not dull as fast. Probably adds to the accurate cutting.

-- The Carpenter Bee is derived from the Ancient Greek word wood-cutter "xylokopos/ξυλοκὀπος"

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therealSteveN

3910 posts in 1087 days


#7 posted 06-15-2019 03:01 AM

They are a tool designed for the building trades. The Festool was the first with anything of an eye toward specialty trim. Take any of them and firmly grasp the deck, and take your other hand and grab the handle. Holding the deck still, just move your handle hand back and forth a little bit. LOTTA flex going on there, and that range of places it can come down, as you change your grip, angle of your forearm, the angle you come down, virtually any movement will be different, and each different is a messed up cut if you are looking at accuracy. That is just a chop style Miter saw, jump up to a slider, and all that flex goes up at least 10%, probably more like 30. Simply because you have introduced more movement, with the slider, Glide, what have you. Lumber cutting tools. In the shop, make rough cuts with them, when you are allowing an inch overage.

You don’t get that “flex” on a TS. You might get a degree or 2 of deflection if you use TK blades, but I am not going to suggest a TK blade if you want real accuracy. TS’s make the best, most accurate cuts in the woodshop. TS’s with a tight sled can increase cut quality quite a bit.

Some folks with really expensive CNC machines say I’m full of beans, those guys may be right, they may be more accurate. If they know how to drive the software.

-- Think safe, be safe

View Bantam's profile

Bantam

6 posts in 132 days


#8 posted 06-15-2019 08:28 AM

Hi Holbs. Good point. Just went to workshop and carefully pulled saw over the same oak test piece just kissing the surface and ended up with a kerf maybe 1/32 or so deep. Testing this with a square it appears spot on however then proceeding through the piece leads to the out of square condition. A new and better blade does seem to be the way to go. Things can only get better, right.

Hi therealSteveN. This is a sliding saw and the sliding bearing/deflection in the slide arms is another source of deflection. The new blade may help a little but it does look like for the accuracy I’m looking for the table saw or shooting the end grain after rough trimming to length. Also sorry but newbie question – what’s a TK blade?

View Jim Finn's profile

Jim Finn

2745 posts in 3434 days


#9 posted 06-15-2019 10:07 AM

The saw blade that came with my Bosch was terrible! I replaced it with a DeWalt blade and it is accurate enough to suit me. I agree that my self made sled for my table saw is more accurate.

-- No PHD just a DD214

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therealSteveN

3910 posts in 1087 days


#10 posted 06-15-2019 11:27 AM

Chopmaster leaves a 7/64 kerf, so 0.109375. They do not give plate thickness, as most suppliers do. I’ve always assumed they don’t want you finding out a lot of blades are thicker. What a Chopmaster is, is well balanced, with great carbide, and a 80 or 90 tooth count. So your cuts will not be frayed.

On the Bosch blade. I am not finding the spec blade for that saw. You could get it off the blade, and google it to Bosch, to see if it isn’t maybe a thicker kerf than the Forrest blade. If the kerf is thicker, stands the reason the plate will be also. With this it does say for that saw it’s a 60 tooth blade, so tooth upgrade, maybe thicker saw plate???? Still not gonna matter on accuracy, it is really a different set of facts. But the slices will be smoother.

I’m just not sold that is going to be enough difference to magically make this a super fine cut tool, but I know it will cost you either 175 bux, or 195 depending on tooth count on the Chopmasters. Don’t get me wrong. I bought one, still didn’t make it tight cutting, it’s the machine, not the blade. Sure you can improve the blade, but it will not become some fine woodworking demon.

Holbs does bring up good points on tool operation, but just tool operation isn’t going to make the difference. It’s a rough cut wobble machine, gonna do what it does. I’m also not poking fun at the Bosch tools, next to the Festool it would be the #1 choice for me. I do own one, but my BIL seems to be using it all the time now. I have a POS DeWalley, but to cut to rough length, it works as good as the Festool.

If you really do want to increase the saw plate, and tooth count I would suggest you go here Kerf is .116, Saw plate is a heavier .098. This blade does NOT deflect, cut quality is very good, maybe not as special as the Chopmaster, but for the $$$$ a much better bargain if you want a stable blade, built on a substantial saw plate.

-- Think safe, be safe

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Bantam

6 posts in 132 days


#11 posted 06-15-2019 05:37 PM

The manual for the saw says that the blade thickness is 2.0 mm (roughly 0.080”). A quick check on the kerf shows it to be about 2.0 mm so thickness here might refer to the kerf with the real plate thickness being less than this due to the set of the teeth. Also I cut some thicker timber and the saw is also showing similar levels of out of squareness in the “chop” plane, so blade deflection in the cut is looking more and more a probability.
Thanks for the saw blade explanation. Checked up on the Freud blade you recommended and it seems to be getting good reviews so I think I’ll give that one a try. Thanks again.

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PCDub

148 posts in 756 days


#12 posted 06-16-2019 01:28 AM



..... – what s a TK blade?

- Bantam


“thin kerf” blade

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