Machine set up

[p111dom]

My problem is this. Setting up 90 degrees on the table or mitre saw is easy. Engineers square on to the sliding table fence, adjust, tighten and there you go. My table saw probably out by 5-10 thou over the distance of the blade according to the calliper. This equates to around half a mil over a 3 foot length which for me is good enough. My mitre saw even less.

However I'm working on a project that requires gluing up octagons and I'm having trouble with the fit. Cuts on the table saw are probably out by 0.05 of a mil over say 100mm widths but 8 pieces cut at 22.5 degrees requires 16 cuts which means a this 0.05 becomes 0.8 of a mil at the end. The same with the mitre saw. You adjust the fence square with the blade on my saw but still if you’re out even slightly cuts like this show up any inaccuracies straight away. I could use an engineers 45 degree square but think I would still have the problem. Am I missing an easier more accurate way of setting up 45 cuts on my machinery? .

(Appologies for mixing imperial and metric units)

 

[Nick W]

The most accurate way is to cut 8 sample pieces, put them together, assess the error, adjust and repeat until good enough.

Alternatively if you have a router table, get a 22.5deg cutter.

 

[p111dom]

Would use the router table if the stock wasn't 4 inches wide. Would need a cutter 100mm high and probably 150mm across! Have been cutting the samples using scrap MDF but it's messy and time consuming. Is there not say an angle measuring laser device where you can pick your angle and adjust or do such things only exist in sci-fi?

 

[beech1948]

A way to poroceed would be to cut out 7 pieces at 22.5 degrees and dry assemble. Then to measure the remaining piece and cut to measurements and not to a pre-determined angle. This way the final piece will be a custom fit into the rest and any minor deviations of size will not be noticed.

regards
alan

 

[Nick W]

Alterntatively, glue up two sets of four, plane the mating surfaces of each set flat, and glue the two halves together. But that's cheating.

 

[p111dom]

Am all for cheating! I have ended up doing as suggested making all the cuts preset except for the last one having to re-cut it on the mitre saw. The supprising thing is that to get a good fit I only needed to add a 1/4 of a degree to close up the final 0.8 of a mm gap. I was surprised that such a small ammount of angle would rectify a relativly large gap. To set up the fence to not have to do this would require an adjustment of 0.015 of a degree which is tiny. I presume this error is due to using a 6 by 4 ich square over a 12 inch blade. I do have a 9 inch square but it's difficult to use on the mitre saw especially when setting the vertical angle. Even with test cuts to set then fence I doubt I could move the fence to within a 100th of a degree. This is not at preventing me from building but it is annoying with a £1200 table saw and a £400 mitre saw!

 

[OLD]

Just of the top of my head if you cut up large widths of sheet material then put them back together along a straight edge you can get your 90 cut perfect and you have 2x90 set up pieces. Then you expand this idea still using wide sheet for accuracy to set the angles you want and use these set up pieces to adjust your machines spot on every time .

 

[engineer one]

you could of course make a shooting board, and then add an angled
board so you can shoot the angles on the boards with a hand plane.

having had trouble initially with the shooting board, i today hand shot some short tapers on the bottom of the legs for my table. on all 4 sides :roll:

paul :wink:

 

[Anonymous]

snip
I presume this error is due to using a 6 by 4 ich square over a 12 inch blade.
snip

To set a fence really accurately you need guess what; a set square, the bigger the better.
To be spot on make your own from MDF with a biggish base against the fence say 600mm. Work out the lengths of the other 2 sides by trigonometry (calculator or trig tables). Draw it up; pencil, straight edge and beam compass for the radii (lath with holes or nicks for pencil and panel pin). Set the fence to cut near the desired line, say 10mm away, and you will be able to see the deviation and make fine adjustments to the fence, with several trial and error attempts getting closer to the line without actually cutting it away.

cheers
Jacob

 

[devonwoody]

How nice to hear from you again Mr. Grimsdale.

 

[p111dom]

Did think about working it out by triganomitory Mr_Grimsdale
but again it's impossible. You simply can't make a pencil mark to within 0.15 of a mill never mind line a fence up to it and how do you suggest I cut the MDF set square out? Presumably with the machines that aren't cutting square in the first place. Mainly it's a problem of distance. Its easy to set the table saw fence parallel to the saw blade using a digital calliper but not so easy to set the sliding table mitre fence square to it. What I really need is to slide the fence as far left as possible so it meets the mitre fence and set it using a set square. I have tried this before with little sucess but that was with a 6 by 4 inch set square. I'll try it with a newly aquired 9 by 6 engineers square. Squares any bigger that this seem to be in the region of £80 what is why I ask if there's an easier way.

 

[inventor]

I do like the idea of cutting 7 the same and then custom fitting the eighth. However, trying to be clever, how about this?

Cut eight chunks of thin MDF, maybe 6mm thick.
Stack them all on top of one another in a neat pile.
Set the saw to your best guess at 22.5 degrees.
Cut the pile of MDF in one go.
Assemble the bits of MDF into the desired shape.
If it doesn't fit, adjust the saw a little, stack up your MDF pile again, and have another go.
Repeat until dinnertime.
Finally, cut the bits of wood you really want, one at a time.

 

[Anonymous]

Did think about working it out by triganomitory Mr_Grimsdale
but again it's impossible. You simply can't make a pencil mark to within 0.15 of a mill never mind line a fence up to it and how do you suggest I cut the MDF set square out? Presumably with the machines that aren't cutting square in the first place. Mainly it's a problem of distance. Its easy to set the table saw fence parallel to the saw blade using a digital calliper but not so easy to set the sliding table mitre fence square to it. What I really need is to slide the fence as far left as possible so it meets the mitre fence and set it using a set square. I have tried this before with little sucess but that was with a 6 by 4 inch set square. I'll try it with a newly aquired 9 by 6 engineers square. Squares any bigger that this seem to be in the region of £80 what is why I ask if there's an easier way.

As described you make your own square i.e. triangular set square. It's not a problem and is a common solution to this sort of thing. Have another go - get the lengths of the sides correct to 0.5 mm and mark up carefully.
The other answer to this sort of prob is to accommodate the (small) error in each joint instead of allowing it to accumulate as a big error in the last one - so it's down to how you hold the pieces whilst you glue them.
Or are you getting the lengths wrong perhaps?
The one definite thing you really don't need is to buy another bit of kit.

cheers
Jacob

 

[ike]

You simply can't make a pencil mark to within 0.15 of a mill never mind line a fence up to it

granted.

and how do you suggest I cut the MDF set square out?

Simple. Get your square square with the aid of a straight edge (saw fence?) and a pencil. Place the square against the fence and mark a line. Reverse the square and mark another line. Plane the edge as required and repeat the above until you get the lines parallel. All of 5 minutes - then it's square enough. :wink:

cheers,

Ike

 

[Steve Maskery]

Alterntatively, glue up two sets of four, plane the mating surfaces of each set flat, and glue the two halves together. But that's cheating.

It might be cheating, but it's what I'd do.
S

 

[p111dom]

I appreciate all the advice but if I plane anything by hand I would be staggered if I could get within a tolerance of 0.015 of a degree which the accuracy I have now and even thats not enough. So are you really telling me you can make a square better than this tolerance using a pencil and a hand plane? On a normal 90 degree cut the set up is close enough but not accurate enough to cut an 8 sided shape requiring 16 cuts.

 

[engineer one]

proper use of a shooting board will get you the closure you need, but i understand your reticence to believe same. :?

as for making the other tools more accurate, there are two thing to think about. one is not to move either fences after setting square, which is of course pretty difficult, the other is to check out the scrit method of setting a table saw, which involves cutting a piece of mdf on all four sides.

maybe that should be a sticky :twisted:

paul :wink:

 

[RinkyDinky]

Anyone got the link to Scrits method of table saw adjustment, have been looking for it for a while.. :?

 

[Mike.C]

Hi Rinky, nice to see you back again, how is the saw going?

Cheers

Mike

 

[RinkyDinky]

The saw is just great, made a mobile base for it, cuts beautifully. I love it!

I added a digital vernier gauge i picked up off fleabay, made by Wixey, it works very well and was really easy to fit, and now the mitre slot is 3/4", have added an Incra gauge and tenon jig.

My wife despairs at the constant tinkering!

Are you happy with the SIP 12" ?

Nice to hear from you Mike, and sorry to hijack the thread!