# Bosch GCM12SD Miter Saw - Squaring Problems (And Solution)



## GrizzlyBagWorks (Jan 16, 2014)

I've spent probably the better part of 3 hours trying get this thing to consistently cut square. Sometimes it wanders half a degree to the right, sometimes half a degree to left. The problem is stemming from the fact that the blade/table shifts relative to the fence when you tighten the locking dial on the end. Has anyone experienced this or heard of it? I've heard of all kinds of other issues including the table not being flat, the glide arms not tracking straight, etc. I've know that other guys have had issues getting it to cut square but I'm wondering if it's related to the glide arms or the table movement.

Anyway, if you guys have any ideas I'm all ears. I'm tempted to pull the saw apart and have a closer look at the locking mechanism to see if perhaps it was cast/machined incorrectly. I'm suspecting it might be thicker on one side vs the other, which would create a wedging effect and shift the table bed. I'll update the thread as I figure more out.


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## JAAune (Jan 22, 2012)

If it's new, return it. The only glider I'd trust for accuracy is the Festool. The others are large-capacity tools for cutting boards on the construction site and not precision tools. If you need precision, I'd advise avoiding the sliders and getting a fixed saw instead.

Awhile back I used a DeWalt slider and it never cut square if I let the saw move on the tracks.


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## JAAune (Jan 22, 2012)

Of course if it is brand new, you could just have a terrible blade.


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## GrizzlyBagWorks (Jan 16, 2014)

Unfortunately I'm beyond the return period. I bought it a few months back when my wife and I built an outdoor table and bench set and needed the extra cutting capacity of this Bosch. I used by Metabo KGS255 for precision work (8.5" CSMS) and the Bosch was 'good enough' for that project. Well, I thought it was a little redundant to have two miter saws so I sold the Metabo a couple days ago and went to dial in the Bosch. That's when I found out how bad it actually was. I should have checked it before selling my Metabo! Oh well.

The Kapex was tempting but I heard way too many stories about motor failures on FestoolOwnersGroup.com Plus the cost was more than 2x, so I couldn't justify it. The glide is stiff and the cuts themselves are straight and glass smooth, it's just the table that's moving. So frustrating.

I tested the saw with 2 aftermarket blades, an Irwin 72t and a brand new 80t Diablo. The blades are good and the Diablo leaves an excellent, smooth and straight finish (as good as my TS55).


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## GrizzlyBagWorks (Jan 16, 2014)

Anyway, I tore the machine apart to get a better look and part of my assumption was correct. There was also another component to this that I didn't consider. The video better explains it. I'm going to drop some metal shims on each side of the large locking block and lightly file the face of it so it contacts the walls of the guide trench as square as possible and as close to the center as possible. I'm also going to lightly sand down the inner guide trench and get rid of the small dents in the aluminum.

The components that squeeze the guide trench really should be curved to match the profile of the guide trench. The fact that they're straight means that the contact area is small and the pressure exerted there high, which combined with the soft aluminum with leave small divots. This is no good. I'm considering order these to pieces build up some steel on them with my tig welder and then filing them smooth to match the round profile. The fact that I have to do this is absurd though….


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## Woodchuck2010 (Jan 19, 2016)

WOW! Totally opposite experience than my Bosch GCM12SD. It was extremely accurate out of the box. Reviews were great for it, so I bought it. I've had it about a year and use it for most of my crosscuts. I think yours is the exception. I'd call Bosch and see what they have to say. There is a warranty on it.


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## GrizzlyBagWorks (Jan 16, 2014)

Well, the good news is that I was able to fix the problem of the shifting bed. I had to modify the pieces in the lock down assembly and sand the guide groove smooth but it's working well. After adjustment I'm only .00125"-.00175" out of square over 10.5". If I set up a dial indicator on the end of the arm and I get it even better but I'm happy as is.

The problem that I was having was stemming from the fact that I used the saw (and the table tightened) when the saw was slightly out of square. When I'd try to move it to the left or right to properly square it the locking mechanism would would slip back into those original impressions. That's why it was inconsistent and different angles. Some angles had deeper/more divots than others, so it was totally unpredictable.

What's critical for new owners here is that you get your saw aligned immediately from the outset, before any impressions are made into the base of the machine. If you're buying a used saw, or have used your own before checking for square, you're going to have to make this modifications.

Bosch really should have either made these steel clamping peices to match the contours of the guide trench. Or keep the shape as is but make them out of a composite material that is softer than the aluminum so that it doesn't dent the base of the machine. I'll update with another video. Mine is performing flawlessly now, but it took a serious amount of effort. I need to address the dust collection now as well.


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## waho6o9 (May 6, 2011)

Awesome, glad you have it figured out.


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## peter_horn (Sep 22, 2015)

GrizzlyBagWorks, I'm thinking about buying this saw. Do you think I could avoid this problem by putting a very thin plastic tape between the clamp thingy and the curved groove?  I'm thinking the plastic might soften things a bit. Steel to plastic to aluminum instead of steel to aluminum. That might not let the steel dent the aluminum.


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## peter_horn (Sep 22, 2015)

This kind of plastic tape.


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## ArtMann (Mar 1, 2016)

That is an interesting observation and makes a lot of sense but my saw doesn't have the problem. What you are illustrating looks to me like a design flaw. That being the case, why don't they all exhibit this problem?

The observation I have made is that it is important to push the blade into the wood without putting any lateral force on the carriage. Lateral support isn't as good as it could be. I have seen this problem on other sliders I have owned or used.


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## BigDuke6 (Oct 12, 2016)

Resurrecting an old post here. I think i have the same issue. Did your fix hold up over time? Any tips on the breakdown of the saw? Thanks for posting this video, thought I was the only guy that couldn't square this .


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## Unknowncraftsman (Jun 23, 2013)

The manuel has good instructions for adjusting the saw. Before you start wrenching on your new saw be sure you have a square that's accurate.And not something that's good enough or you be chasing your tail.
Also keep in mind thats a big blade for a light weight saw.Some materials are going to push the blade around dense thick wood even Plunge cutting down in to plywood is not a good test for the saw.
I do have one.
It a good trim saw for cutting tall moldings for solid wood it's ok.


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## GrizzlyBagWorks (Jan 16, 2014)

@bigduke6 , the modification worked in that if fixed the movement/shifting of the bed when locking everything down but the saw still wasn't repeatable. I ended up selling it to someone that didn't care about it cutting dead square. Between the squaring problem and the poor dust collection I just couldn't justify keeping it. I went with a Hitachi c10fch2 and have been much happier with the accuracy of this saw.


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