Saw blade and mitre slot misalignment question

[Robb]

Hi guys

I've just been tuning my table saw up (its been a while!) and have realised that I have 0.3mm (0.015") inaccuracy between the blade and the mitre slot (i.e. the blade is not 100% aligned to the mitre slot.

What is too much? What would you accept on your saw?

Just interested

I've put a poll at the top of the post

 

[OPJ]

I think this largely depends on how much you have payed for your saw. Unless you've spent a few thousand on a top-of-the-range panel saw (brand new), I think this is acceptable.

 

[Bean]

Mmm I disagree.

I would check to see how flat the blade is first, Then how much error I could induce with the set up for clocking the blade. The try to eradicate those errors as much as possible.

Once you have all the figures you will then have an idea of the run out of the mitre slot to the spindle (blade).

You may find that your saw is far more accurate than you think, then again it could be worse. It may just be me but I would not stop at at 0.3 (0.015") I would continue working on it until I get into the low thou's 0.004" or so.

 

[Robb]

Hi Bean, agree re blade deflection. I 'think' I managed to eliminate it from my calculations though. Not sure.

The blade has a deflection of 0.004 in total (-0.001 to 0.003) which, from what I have read in my handy table saw book, seems acceptable.

I followed a rather fiddly process (fiddly because I'm inept with a dial gauge and associated paraphernalia) but I marked the blade, attached the gauge to my mitre gauge, measured the blade at one end and then pulled the gauge back, brought the blade round to the mark and measured again. Gives me a measurement along the plane of the mitre slot at the same point on the blade.

I 'think' that means I have have eliminated the blade inaccuracy from the measurements, as I measured from the same point on the blade.

It's certainly not the 'most' fun part of the hobby for me, but its hugely satisfying. I think it resolves to the inner geek in me!

Hi OPJ, it's no top of the range saw for sure. I'm just sure I can hear the back of the blade cutting as the wood exits. I've done the fence accuracy once, maybe its time to return to that as well!

It will be interesting (to me at least) to see what other woodworkers think is acceptable, s'pose it depends on what your using the saw for!

 

[Rich]

Hi Robb, having used a DTI, I guess you are used to precision measurements, have you tried adjusting the trunnion? regardless of the value or worthiness of your tablesaw, there is no reason why it should not be exact, I'm sure with a tad more fettling you will be spot on, settle for nothing less.

Rich.

 

[Bean]

I followed a rather fiddly process (fiddly because I'm inept with a dial gauge and associated paraphernalia) but I marked the blade, attached the gauge to my mitre gauge, measured the blade at one end and then pulled the gauge back, brought the blade round to the mark and measured again. Gives me a measurement along the plane of the mitre slot at the same point on the blade.

I 'think' that means I have have eliminated the blade inaccuracy from the measurements, as I measured from the same point on the blade.

It's certainly not the 'most' fun part of the hobby for me, but its hugely satisfying. I think it resolves to the inner geek in me!

Robb yes DTI's can be a bit fiddly, but there is no reason why you should not get a very close alignment.

Have you checked that the fence is straight? The ends may be parallel to the mitre slot, if measured as some suggect by checking each end, I prefer to check along the full length of the fence with the dreaded DTI. Its worth a look as a bow in the fence can cause simular effects.

 

[Robb]

Bean, first job tomorrow I'll get a straight edge on the fence, hadn't considered a bow, just checked both ends were on the mitre slot, with a 1mm slope away from the blade at the far end.

Rich, the trunnion is kind of where I am now at. I stood and looked at the saw this evening and wondered if I embarked on the trunnion would I make matters worse than the current slight inaccuracy. It's actually what prompted my post in the first place.

I think it's inevitable that I'll go at the trunnion, the front bolts are so heinously inaccessible though (its an xcalibur saw, pretty much a Delta contractor saw copy) so accuracy is definitely in the bounds of possibility.

I'll let you know when I manage to get it even more inaccurate than it is now

Thanks for all the replies and help guys, appreciate it.

 

[devonwoody]

I owned a German table saw once, and when you wound the blade up and down the distance changed. (the blade went sideways) So it might even pay to see what measurements you get at different blade heights.
Havent voted because I think it depends on the saw quality.

 

[Benchwayze]

Yes the sawblade must be parallel to the mitre-guide channel. If it isn't so, you can't rip accurately and you can't crosscut accurately using the mitre-guide either.
But even the cheapest saw should have a table that is adjustable around the blade.

I always try to get my blade as close to parallel as I can. After that it's watching how the saw performs and noting if there's discrepancy creeping into your work, if you use the saw for jointing. The better the blade though, the easier it is to make and retain the adjustments. A superior blade works wonders on the humblest of saws.

BTW, I don't use dial-guages. I find that's a sledgehammer to crack the proverbial. I use a piece of wire, blu-tacked to the mitre-guide. Then measure the gap between blade and wire with a feeler-guage. When the measurement is the same at the rear of the blade as the front, I rotate the blade 180 deg and check again. With a good blade the measurement will be the same. Line the fence with the slot and if your fence is straight, then job done.
HTH

 

[motownmartin]

Mine is less than 15 thou but i'm still not happy with it as I still get of back cut and pulling away from the fence.

I must take a bit of time one day to get it right, I think it will make all the difference and produce a finished edge.

 

[Niki]

I use a little bit different method for the final (fine) "Blade/Miter slot" and "Miter slot/Rip fence" and, the alignment becomes perfect...I use what I call "Dynamic check" i.e. the blade is rotating at normal speed so all the "Arbor Run-out", "Blade Run-out" and all the others are "included"...
And no, I don't use any measuring equipment for the fine tune but, it cuts perfect squares...

niki

 

[maltrout512]

This isn't the link I was looking for but, seems to have the relevant details.

http://www.newwoodworker.com/basic/tsalign.html

 

[devonwoody]

Nice one Malcolm, have you visited the video section of this web page?

Its good.

 

[Robb]

Thanks for the link Malcolm, more handy info.

I didnt get into the workshop today, but hopefully I'll get things sorted this week with all the advice from above.

Thanks guys, appreciate it

Robb