Bosch GCM 8 SJL detents out

[Jezza42]

Hi guys
The detents are out on my Bosch GCM 8 SJL Mitre Saw.
Are they adjustable?
Am i missing something, but i cannot see a way of adjusting them?
I think it’s poor design for a £300 saw if they cannot.

Regards Jezza

 

[Deleted member 174758]

I had a quick look at the GCM8JSL. What i found was that the detents are actually cast into the underside of the turntable (meaning that when they wear the angle settings become sloppy, in which case a new turntable baseplate is required - part 840 sku 1 609 B03 744.A5 at £200 or so, ouch!). This looks like a similar design to the one adopted by Makita for many years and I can tell you for certain that they do eventually wear - but it does take a LOT of use. But they can't be adjusted on any saw

If on the other hand the is that the 45 and 0 degree detents are inconsistent side to side I'd first recommend checking the face of the cast alumimium horseshoe fence for straightness using a good quality straight edge, such as a spirit level in conjunction with some feeler gauges. It is possible that the fence is "cupped", in which case you will need to fix something like plywood auxiliary fence plates which are screwed through the back of the existing fence plates and then packed to.be straight. This is a very common fault with mitre saws - two of my Makita mitre saws have suffered from this problem as have a couple of hired in deWalts and a hired in Milwaukee, so it isn't peculiar to one brand

If that is sorted you then need to check the fence for cutting square by doing a "self-checking cut": basically take a piece of parallel sided timber such as 4 x 1in skirting and make a cross cut. Leave the left hand piece of timber on the bed of the saw. Flip the right hand piece over, bottom to top. Slide the two together. If there is a gap at the front, the saw is cutting to the left and the RH end of the fence needs to be adjusted backwards a touch (or the LH end forwards). Conversely, if there is a gap at the rear, the saw is cutting to the right and the LH end of the fence needs to be adjusted backwards a touch (or the RH end forwards). Make the adjustments and try again. Repeat until it is cutting square. Warning: this is a fiddly process, but is far more accurate than using a square to check the saw

Once you saw is cutting dead square you can check the 45• mitre cuts. Similar process using a piece of 4 x 1 or the like, only you make a left mitre cut then offer up the two pieces on a flat surface with one of them flipped over to form a letter "L". The outside is checked for squareness with a validated try square (that is important). You repeat the exercise for the other mitre angle.

Do this and you will know how accurate your saw is. Whilst saws are supposed to come from the factory set to cut a perfect square cut, but they do get carted around the world a bit before they get to you, so they aren"t always right.

 

[Jezza42]

I had a quick look at the GCM8JSL. What i found was that the detents are actually cast into the underside of the turntable (meaning that when they wear the angle settings become sloppy, in which case a new turntable baseplate is required - part 840 sku 1 609 B03 744.A5 at £200 or so, ouch!). This looks like a similar design to the one adopted by Makita for many years and I can tell you for certain that they do eventually wear - but it does take a LOT of use. But they can't be adjusted on any saw

If on the other hand the is that the 45 and 0 degree detents are inconsistent side to side I'd first recommend checking the face of the cast alumimium horseshoe fence for straightness using a good quality straight edge, such as a spirit level in conjunction with some feeler gauges. It is possible that the fence is "cupped", in which case you will need to fix something like plywood auxiliary fence plates which are screwed through the back of the existing fence plates and then packed to.be straight. This is a very common fault with mitre saws - two of my Makita mitre saws have suffered from this problem as have a couple of hired in deWalts and a hired in Milwaukee, so it isn't peculiar to one brand

If that is sorted you then need to check the fence for cutting square by doing a "self-checking cut": basically take a piece of parallel sided timber such as 4 x 1in skirting and make a cross cut. Leave the left hand piece of timber on the bed of the saw. Flip the right hand piece over, bottom to top. Slide the two together. If there is a gap at the front, the saw is cutting to the left and the RH end of the fence needs to be adjusted backwards a touch (or the LH end forwards). Conversely, if there is a gap at the rear, the saw is cutting to the right and the LH end of the fence needs to be adjusted backwards a touch (or the RH end forwards). Make the adjustments and try again. Repeat until it is cutting square. Warning: this is a fiddly process, but is far more accurate than using a square to check the saw

Once you saw is cutting dead square you can check the 45• mitre cuts. Similar process using a piece of 4 x 1 or the like, only you make a left mitre cut then offer up the two pieces on a flat surface with one of them flipped over to form a letter "L". The outside is checked for squareness with a validated try square (that is important). You repeat the exercise for the other mitre angle.

Do this and you will know how accurate your saw is. Whilst saws are supposed to come from the factory set to cut a perfect square cut, but they do get carted around the world a bit before they get to you, so they aren"t always right.

Thanks for the reply.
This saw has two separate fences, not the horseshoe type (not sure if that’s a good or bad point)
I’m going to purchase some 5 thou shim washers and try and pack one of the fences out to exactly 90 degrees to the blade, then do the other fence in line with the “true” fence, then check the 45 degree detents again.
If they are still out i feel i need to bin the saw and purchase another with an adjustable detent plate that can be set up correctly.
Are there any brands you feel i should avoid?
Thanks for your advice, much appreciated bud

Regards

Jezza

 

[Deleted member 174758]

Sorry to say, but all the spares drawings I have looked for the GCM8SJL, like these ones (part no. 24), clearly show a 1-piece horseshoe fence with a sliding fence plate on either side. Is your saw different?

As I say you can't begin to adjust the mitre angles until you have checked, and if needs be corrected, any errors in the fence plates. The fence appears to have three holding bolts, similar to the Makitas and deWalts I am familiar with. Do they go through oval holes (or rather do the pair on the RH side go through oval holes as I suspect leaving the LH hole as a pivot point? DON'T remove both at the same time to confirm this as that risks the fence being moved)

 

[Jezza42]

Sorry to say, but all the spares drawings I have looked for the GCM8SJL, like these ones (part no. 24), clearly show a 1-piece horseshoe fence with a sliding fence plate on either side. Is your saw different?

As I say you can't begin to adjust the mitre angles until you have checked, and if needs be corrected, any errors in the fence plates. The fence appears to have three holding bolts, similar to the Makitas and deWalts I am familiar with. Do they go through oval holes (or rather do the pair on the RH side go through oval holes as I suspect leaving the LH hole as a pivot point? DON'T remove both at the same time to confirm this as that risks the fence being moved)

That’s a different saw bud, that’s the GCM8S not the GCM8SJL, you can clearly see the separate fences on here

 

[mrrusty]

I have this saw and mine is very accurate ...unless you manage to bend the LH pointy end of the fence when a piece of wood grabs because you were doing something stupid (trying to slice down the middle of too small a piece that snatched - yes I was holding with a push stick, but still....). Fortunately a new part sorted that out.

You are using a nice sharp blade aren't you? I have found a blunt blade does run out a smidgen - must be some flex somewhere