LumberJocks

Circle Cutting Jig ( for the bandsaw) #2: Of slidey things

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Blog entry by BritBoxmaker posted 02-06-2011 09:16 PM 2514 reads 1 time favorited 8 comments Add to Favorites Watch
« Part 1: The urge for greater accuracy Part 2 of Circle Cutting Jig ( for the bandsaw) series Part 3: Recent modifications »

Right having got the sliding table to run in it’s runners properly, with the application of some wax, the next thing to do is install an 8mm ‘T’ nut into the jaw end of the sliding table. thus
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The rod will be captive in the left fixed table and so any rotation of it will now be transmitted by the ‘T’ nut into movement of the sliding table, to and from the blade position. The one on the top of the sliding table is just there to show you what the ‘T’ nut looks like. I then located the guide pin (for centre of circles being cut) in the top left part of the sliding table. This was done by setting an M6 ‘T’ nut into the top of the sliding table
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and screwing an M6 roofing bolt through from the underside. Note the recess to allow the head of the bolt to clear the base board. The centre of the bolt is aligned with the front edge of the bandsaw blade, when viewed from the right hand side of the bandsaw.
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I then cut off the excess from the right hand end of the table and cut a 2mm slot through the rear half of the jig to allow the bandsaw blade to enter the jig in use. I also installed a guide across the bottom of the jig to run in the bandsaw table mitre guide slot (not shown, forgot to take picture).
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and attached a 10mm Beech trim strip to the left hand end of the left fixed table.
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You will also see that the trim has an appropriate hole for the adjusting rod to pass through and a 3mm deep slot cut into it to take the captive rod plate. In order to make the rod captive I needed something for the plate to act against.
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I’m quite proud of this. All it is is two M8 nuts tightened against each other, so they lock, which is then rounded down to 12mm on a bench grinder. Its place on the rod is such that the rod goes all the way from the right hand end of the sliding table to sticking out by 50mm to the left of the left fixed table. To house this I over-bored the rod channel to 13mm, 12mm deep at the left end of the left fixed table.
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I then installed the captive plate. Its 3mm mild steel. Shop made with hand tools. The rod hole is 8.5mm and the bottom holes are for fixing. I placed a washer on the rod followed by two back to back locked M8 nuts.
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- Making sure that the rod still turned freely. Rotating the rod now moved the sliding table. With this working the first job for this jig was to cut it’s own adjustment wheel. Two pieces of hardboard (masonite) glued back to back.
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The scale, stuck to this is from a project by rmac and many thanks to him for it and making my job easier
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Here are all the things that make up the adjustment assembly. Laid out in order on the sliding table.
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The captive plate, washer and two nuts are already installed. Next on is the adjustment reference plate. Made of 3mm Perspex (Plexiglass), complete with spacers.
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Finally the adjustment wheel goes on, backed off bu a washer and two back to back locked M8 nuts. The whole assembly seen from the front.
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This is what the finished jig looks like (after you complete the trim work front and rear)
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In part 3 we see the modifications I have made to this jig

Be seeing you

-- Martyn -- Boxologist, Pattern Juggler and Candyman of the visually challenging. http://www.theartofboxes.com



8 comments so far

View degoose's profile

degoose

7052 posts in 2109 days


#1 posted 02-06-2011 09:32 PM

Great concept… how big can you go…??

-- Drink twice... and don't bother to cut... @ lazylarrywoodworks.com.au For lovers of all things timber...

View BritBoxmaker's profile

BritBoxmaker

4448 posts in 1790 days


#2 posted 02-06-2011 09:39 PM

Thanks, Larry I forgot to mention some specifications for this jig.

Size – 750mm x 400mm x 30mm.
Circle cutting range – 25mm to 450mm radius (50mm to 900mm diameter)
Positional accuracy – +/- 0.05mm

Let me explain the accuracy figure. Thread pitch for M8 is 1,25mm. There are 25 divisions on the scale making one division 1.25/25 = 0.05mm travel.

I know run-out on a bandsaw blade may be greater than this but it is positional accuracy for successive cuts from the same workpiece I am interested in.

Also glue used throughout was PVA and the jig was finished in Oil (with the exception of the underside and runners of the sliding table which were waxed).

You should also clamp the jig down to the bandsaw table for safety reasons.

-- Martyn -- Boxologist, Pattern Juggler and Candyman of the visually challenging. http://www.theartofboxes.com

View tdv's profile

tdv

1130 posts in 1824 days


#3 posted 02-06-2011 11:33 PM

Thanks for posting the dimensions Martyn I think this has to be well on the way to being the ultimate circle jig
I will make one copying your design if you don’t mind? I made a vesion like Norms (remember him ?) & it’s poor, to say the least. The only good thing is the built in folding height adjustable leg it’s a good support for larger diameters
Cheers
Trevor

-- God created wood that we may create. Trevor East Yorkshire UK

View BritBoxmaker's profile

BritBoxmaker

4448 posts in 1790 days


#4 posted 02-06-2011 11:47 PM

Norm, who is he? No seriously who is he?!

Copy away Trevor and thanks for feedback and help with the chipout problem.

-- Martyn -- Boxologist, Pattern Juggler and Candyman of the visually challenging. http://www.theartofboxes.com

View steliart's profile

steliart

1816 posts in 1442 days


#5 posted 02-07-2011 12:36 AM

Thanks Martyn, now I have a better view of the jig and its mechanism.
Stay safe
Steli

-- Stelios L.A. Stavrinides: - I am not so rich to buy cheap tools, but... necessity is the mother of inventions - http://www.steliart.com --

View BertFlores58's profile (online now)

BertFlores58

1646 posts in 1676 days


#6 posted 02-07-2011 03:54 AM

Hi Martyn,
Think of the backlash of the thread. It is not a problem when locked-in during cutting however the guide is good enough that it must be stopped at first touch of the push or pull of the thread… I know you knew this… We call it in the machine shop on any threaded control ….. PICK UP THE SLACK….

Additionally, you can also add kerf adjustment somewhere in you dial or on the sled. This will provide ways at which good side (the edge that will connect to the other) and the waste side (the edge that could be wasted) may it be inner or outer side for proper fit…

This is where the LJ comes in handy… the suggestions are always fruitful…
Cheers,

-- Bert

View SPalm's profile

SPalm

4941 posts in 2636 days


#7 posted 02-07-2011 03:14 PM

Looking good Martyn. Clever ideas in there.

Norm Abram – A PBS legend woodworker and house fixit guy.
The New Yankee Workshop
http://en.wikipedia.org/wiki/Norm_Abram

Steve

-- -- I'm no rocket surgeon

View mafe's profile

mafe

9693 posts in 1843 days


#8 posted 02-07-2011 06:33 PM

Hi Martyn,
It is looking really good, and yes some really nice ideas for the detail, I will move on to next part.
Best thoughts,
Mads

-- Mad F, the fanatical rhykenologist and vintage architect. Democraticwoodworking.

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