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Quick question about finger joints

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wizer

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for some reason I can get me head around the maths. so:

for instance, I have 4 pieces of wood 130mmx500mmx15mm

How do I work out the size of the joints? How many joints?

sorry for the dumb question
 

jasonB

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Which edge are you trying to join :?: Width of fingers will be determined by the cutter, divide this into the length of the joint, any odd bits equalled out at either end.

Jason
 

wizer

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I should have mentioned I am doing this on the table saw not the router table.

I want to joint the 130mm sides

When you say any odd bits get equalled out at the end, thats what is confusing me. The calculator says 130 / 6 = 21.6666666

:?:
 

jasonB

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No tablesaw jig will be that accurate so it will probably be better to start from one edge and work your way to the other, Cut the two joining ends at the same time with the boards staggered by the 6mm? cutter, that way you get a matched pair for each corner.

What are you using to get the 6mm cut, a dado?, hope your jig has some guards.

Jason
 

jasonB

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If you do work it out then it goes as follows

5mm finger, 6mm groove, 6mm finger.......5mm groove

other board will go

5mm groove, 6mm finger, 6mm groove......5mm finger

In other words 10grooves + 10 Fingers @ 6mm each = 120mm

130-120=10

10/2 = 5

Jason
 

wizer

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no, no dado. The jig is from the Triton video. I made a sketch of it on paper. It's basically a sacrificial fence screwed to the mitre gauge. All 4 sides are clamped to the sacrificial fence with the middle 2 offset by the width of the first rebate. Then a stopper is used to guage the first rebate. The jig is run through the saw nibbling away the material until it hits the fence.

Does that make sense?


I think I'm following the methodology now.

Thanks very much Jason
 

Noel

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Wizer, unless you are restricted by a particular width of timber I think it's alot easier to forget about calculations. Cut the fingers to your desired size. Just eyeball a size that looks right and never worry about the fingers / gaps on each edge of the timber. Once you've finished cutting just rip and finish the edges so that there is a full finger at each end. As the fingers should / will be identical it's not too hard to do.

Noel
 

wizer

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thanks Noel, why didn't i think of that! ](*,)
 

jasonB

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Wizer, Not seen the triton jig but sounds just like the way I do it on the saw except I make the grooves/fingers the width of the blade kerf (3.2mm)

If you want a tight joint you will need a blade with zero top bevel, I have a Kity rip blade with this grind, otherwise the bottom of each groove will have a "V" shape to match your blade.

Also cut your timber 2mm overlength and the grooves 1mm thicker than the timber, you can then clean up the 1mm projection after the glue has set.

Jason
 

devonwoody

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Wizer

Do some pre runs on scrap timber first.
I dont know which saw you are using on the workcentre but blade height stability could be a problem.
 

wizer

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:? :oops:




Not entirely sure what id did wrong. The gaps are roughly 2.5mm which is the thickness of my blade. I am sure I allowed for this in my setting out... obviously not!

:(
 

wizer

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Right let's see if we can work out what went wrong. Forgive me for thinking out loud.

80mmx500mmx18mm MDF

Joint on 80mm side.

80mm divided up equally into 4 = 20mm tongue and rebates.

Saw blade lowered to just above thickness of MDF

4 pieces of MDF clamped together, middle 2 raised by 20mm. (spacers used for accuracy.)

Pieces up on end against mitre gauge and against fence.

Fence set at 37.5mm (allowing for 2.5mm blade width)

17.5mm Setting block up against clamped pieces then stop block clamped to mitre guage.

Setting block removed

Pieces run through the saw with each pass getting closer to the stop block until all material is taken away.

Fence adjusted to 77.5mm and setting block/stop block shifted up to the work pieces again.

Run through same as before

Flip whole thing over and start again at the other end





It seems to make sense, i'm stumped
 

devonwoody

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When doing them on the router table the first finger is offset otherwise you get two fingers at the same height. 8)
 

wizer

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here's a shot of what I am doing if it helps

 

devonwoody

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Wizer pm me your privatee email address and I will send photocopies zipped of the Triton router system manual for the finger jointer.

Basically you cut the first finger space and then add the second piece to the original but this is offset.
 

wizer

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cheers dw but my router table doesnt take the Triton Finger Joint jig. I'm trying to get my head around this table saw system. Ive seen the guy doing it on the DVD and it works for him. I'm going to have another go over the weekend, see if i can work out my mistake
 

devonwoody

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I think the actual cutting sequence would be the same whether you are using a saw blade or a router bit. Anyway I put the manual pages on my web site tomorrow morning if you still want them. (my server account closes at 4pm and there is nearly 1mb)
 

wizer

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Yes, thank you, i'd be interested in taking a peek DW. I spent the afternoon looking up router table box-joint jigs. I may go down that route, but still a bit frustrated that the table saw mathod didnt work.

I'm sure it was just mis-measurement somewhere. Might run through the process again tomorrow, see how I go.
 

les chicken

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Wizer
Trying to follow your train of thought it is late and I have had a bad day. But I think your problem is :) that you are allowing for the thickness of the blade twice. The setting for the fence should be the actual no allowance for the blade and the stop leave as you have calculated. In other words if this makes sense 40mm to the fence not 37.5. and leave the other stop as is worth a try.
ps You seem to be having fun :lol: I hope you are not disappointed with your purchase.
Les
 

les chicken

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Wizer
Just got myself a whisky made a fuss of Lucky and calmed down. Not sure if the figures i gave you are correct but you are definitely allowing for the width of the saw blade twice.
Les
 
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