SCMS's - Not built for accuracy?

[OPJ]

I've been struggling to cut accurate mitres in 70mm and 40mm wide, 13mm thick American Black Walnut today for a simple serving tray I'd like to get finished ASAP.

I've got the timber stood on-edge, with the face resting against the fence cutting down across the width of the timber with the blade locked (and checked) vertically and 90º, while the saw is swung round the 45º mark.

What I keep finding is that the saw is reluctant to cut a perfectly vertical edge, no matter how slowly and carefully I make the cut. I'm not fussed about the 45º angle at this point, but if it doesn't cut slightly off-square then it cuts in almost a 'curve' shape near the beginning of the cut... Even when I have the timber securely clamped.

I should perhaps mention that my saw is the Bosch GCM 12 SD.

I'm having to resort to cutting them over size and finishing off with a plane and shooting board. Can't imagine the bandsaw will be good enough but I might have a go and see what the disc sander can do... :? I don't have a table saw, I should add.

It's almost like something is 'flexing' during the cut and it happens an awful lot, even when cutting "square", particularly on wide boards.

What about the rest of you, how accurate do you find your mitre saws? Are they purely built for site work?? Maybe it's time to start saving up for a Festool Kapex... If I could get £300 for this saw, say, then that's only £500 to go! :wink:

I'd appreciate anyone's thoughts and experiences on this. Thank you.

 

[gidon]

Olly - I think you're far better off doing as you are doing - finishing off with a shooting board. I've never been happy with mitres directly off my table saw or mitre saw (I have the Bosch 10 SD). It's fine for rougher work but not for really tight mitres in my opinion - even with a good fine blade.
What does your signature mean out of interest?
Cheers
Gidon

 

[OPJ]

You clearly don't watch Heroes then...! :wink: (All I've done is substitute cheerleader for chairmaker - I thought it was clever...)

 

[dennis]

Olly

As I think that this is a compound mitre saw have you tried cutting with the wood flat.

Dennis

 

[Paul Chapman]

I would class an SCMS as primarily a site saw - not really ideal for fine cabinet making. For accuracy, you won't beat a good plane and a shooting board IMHO.

Cheers :wink:

Paul

 

[Steve Maskery]

Olly
Are you trying to trim off a hair at 45 deg? If so, the teeth on one side are all cutting whilst the teeth on the other are not. It's enough to make the blade flex, I've had exactly the same problem. If you cut so that there is proper timber on both sides of the blade then these forces are more balanced.

Fan as I am of Festool, and I would kill for a Kapex, I'm not convinced that you would not have the same problem, as I think it's the nature of the beast rather than a weakness of the Bosch (I have the same machine).

At this point I think your best best is a good shooting board TBH.

HTH
Steve

 

[George_N]

I've been struggling to cut accurate mitres in 70mm and 40mm wide, 13mm thick American Black Walnut today for a simple serving tray I'd like to get finished ASAP.

I've got the timber stood on-edge, with the face resting against the fence cutting down across the width of the timber with the blade locked (and checked) vertically and 90º, while the saw is swung round the 45º mark.

What I keep finding is that the saw is reluctant to cut a perfectly vertical edge, no matter how slowly and carefully I make the cut. I'm not fussed about the 45º angle at this point, but if it doesn't cut slightly off-square then it cuts in almost a 'curve' shape near the beginning of the cut... Even when I have the timber securely clamped.

I should perhaps mention that my saw is the Bosch GCM 12 SD.

I'm having to resort to cutting them over size and finishing off with a plane and shooting board. Can't imagine the bandsaw will be good enough but I might have a go and see what the disc sander can do... :? I don't have a table saw, I should add.

It's almost like something is 'flexing' during the cut and it happens an awful lot, even when cutting "square", particularly on wide boards.

What about the rest of you, how accurate do you find your mitre saws? Are they purely built for site work?? Maybe it's time to start saving up for a Festool Kapex... If I could get £300 for this saw, say, then that's only £500 to go! :wink:

I'd appreciate anyone's thoughts and experiences on this. Thank you.

Have you tried it with the timber laid flat? If you are cutting down through a 70 mm x 13 mm piece in edge there is a lot of scope for the timber to shift/ flex and for any slop in the slide bars to show. If you only have to cut down through 13 mm the timber will be better supported on the bed of the saw and have less chance of it moving on you.
By the way, that is one of the reasons I bought a non-slider (the other being cost)...jus a bit more rigid and so far I haven't needed the larger capacity of a SCMS.

 

[OPJ]

Dennis, you're correct in saying that this is a compound mitre saw (a slider, too) but I find that when you tilt the blade to 45º it's very hard to see what you're doing with a 12" saw! :? Might be worth a shot though.

Interesting point, Steve; I am indeed trying to make my first cut right on the end of the timber for as little waste as possible. Your theory does make sense, though it doesn't perhaps explain why the cut still wanders of when there's timber either side of the blade. :roll:

I'd have thought the Kapex would be better because of the front rails, meaning the 'head' has more support as it travels. This has made me wonder how on Earth some people get on with these saws on-site...! :shock:

The other thought I had waste what if I draw the blade infront of the stock first, switch on and then slowly push it back through the timber - does that sound dangerous? :?

 

[OllyK]

Dennis, you're correct in saying that this is a compound mitre saw (a slider, too) but I find that when you tilt the blade to 45º it's very hard to see what you're doing with a 12" saw! :? Might be worth a shot though.

Interesting point, Steve; I am indeed trying to make my first cut right on the end of the timber for as little waste as possible. Your theory does make sense, though it doesn't perhaps explain why the cut still wanders of when there's timber either side of the blade. :roll:

I'd have thought the Kapex would be better because of the front rails, meaning the 'head' has more support as it travels. This has made me wonder how on Earth some people get on with these saws on-site...! :shock:

The other thought I had waste what if I draw the blade infront of the stock first, switch on and then slowly push it back through the timber - does that sound dangerous? :?

I know the use of SCMS was covered on here some time back and the suggestion was that you should pull it towards yourself. TBH I found a) it didn't cut as well done like that and b) the blade spin caused the arm to push towards me as I was pulling resulting in it often running across the work faster than I would have liked.

Also check the wood you are cutting is dead flat, if it isn't you won't get a straight cut.

Having re-done all the skirting in the house with a SIP 10" SCMS, I have found to be perfectly sufficient for the job once set up.

 

[dennis]

Olly

I have sometimes cut through from the front and never found it dangerous.It is worth trying this and with the wood flat on scrap pieces that are not too short and find which gives the best results and which you feel most comfortable with but whatever method I dont suppose you need reminding make sure your hands are well out of the way.

Dennis

 

[wizer]

I'm confused. Are you saying that you normally pull the blade towards you through the wood?

 

[bob_c]

I bought one of those axminster mitre trimmers a few weeks back and im highly impressed with it,very accurate and would be ideal for the sizes you mention.There a siimilar sized Wadkin one on ebay right now,but dont know what shape the blades are in.link

 

[woody67]

Hey Bob - the Wadkins just down the road from you............bit tempted are we???? :wink: :wink:

Mark

 

[bob_c]

I would have been if i hadnt of bought the axminster.

 

[seaco]

I use a Dewalt DW708 SCMS and really can't fault it I haven't checked it for about six months and did so about a week ago and it was bang on dead straight cuts you can't expect it to cut a finished edge for cabinet making though a shooting board is always going to be the way to go for this...

 

[OPJ]

I raised a similar discussion in another forum and one suggestion that came up was to change the blade. What do people think about this?

The current blade, I believe, is the one that was originally supplied with the saw. There's no indication to say whether it's Bosch's own brand. Someone also suggested cleaning the blade...

So, where to look for replacements? I did flick through the Axminster catalogue and glance at the CMT blades but the prices there have frightened me off! I'm struggling to find 300mm Freud blades. I know Screwfix used to stock them but there isn't much of a selection in Toolstation either.

Any thoughts on this?

 

[seaco]

Hi Olly

Just looking on ebay and found this ebay link

Might help

Lee

 

[OPJ]

Thanks for the suggestion Lee, although I think 48t might be a little too coarse? I did however spot a 96t blade, which is then perhaps too fine, although the price looks good right now.

 

[gidon]

You clearly don't watch Heroes then...! :wink: (All I've done is substitute cheerleader for chairmaker - I thought it was clever...)

No sorry don't - but reguarly told by my sister that I should !

Cheers

Gidon

 

[OPJ]

Well, I may not be your sister, but whatever you do, don't watch tomorrow night's episode as it's the last one of the second series!! :shock: :wink: