LumberJocks

Position counter for screw-driven joint jigs

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Project by Don Johnson posted 01-29-2017 05:07 PM 1833 views 4 times favorited 7 comments Add to Favorites Watch

I recently uploaded ‘My version of Ed Stiles’ box Joint Jig’ http://lumberjocks.com/projects/293986 and a comment from htl about losing count set me thinking about how a counter might be a useful addition to the jig. Initially I thought of an electronic counter as these sort of components are so cheap nowadays, and the display could be positioned in the middle of the jig, and it would look quite smart. However, I quickly realised that to be sure of showing an accurate location – such as when accidentally going past a position and having to rewind back to it – an up/down counter would be needed. This would involve a little logic circuitry, but also a shaft encoder, so with the need for a battery or a power supply, I thought that this was going ‘over the top’.

Whilst looking for electronic counters, my searches also brought up a mechanical version of an up/down counter, and although this would not be as techie it seemed as though it would do the job – so I ordered one. When it arrived it was bigger than I had anticipated, but its large size is an advantage as the display is easier to read. Luckily I had mounted Ed’s ‘clacker’ on the inside of the left-hand support, so it was easy to fit the counter on the outside with a simple bracket, and a collar with concentric holes to suit the counter shaft and the stub end of the jig screw which I had left protruding.

My saw blade is 1/8th inch kerf, and my jig screw has 1/16th inch pitch. To cut 1/8th inch wide ‘teeth’, after setting-up, I make a cut, turn the screw 4 times, make another cut, turn the screw 4 times . . and so on. With the counter set to zero at set-up, it shows 0, 4, 8, etc. each time I make a cut Therefore, instead of having to remember how many turns I’ve made, I can make a card with 0,4,8,12,16,20 . . . printed on it, and use this to tell me that I should make a cut whenever one of these numbers appears on the counter. For an old geezer like me, with a terrible memory, this seems a very simple solution. On the back of the card I can print 2,6,10,14,18,22 . . . so I can turn it over when cutting box ‘ends’ rather than ‘sides’. No confusion between which set of numbers to use – only one set is visible.

For 1/4 inch ‘teeth’ my card would have 0, 2, 8,10,16,18,24,26,32,34 . . . and on the back: 4,6,12,14,20,22,28,30,36,38. Similar cards could be made for 3/8th and 1/2 inch teeth, or any size desired, and with some care in getting the numbers correct, variable sized teeth in one joint.

This approach seems so simple and foolproof that I can’t understand why nobody else has thought of it before – I certainly don’t recall seeing anything like this mentioned in the details of all the other screw-driven jigs that I researched. Have I missed a hidden drawback? Provided Stumpy was prepared to turn his handle all the time instead of lifting his slider, he would not need his coloured square-wave drawings, just a set of cards from which he just has to make sure he picks the right one! As Matthias’s system is so versatile and capable of adjusting ‘tooth’ sizes to suit material width, I don’t think it would be of any use there, nor would it be applicable to John Heisz’s design. Other systems which just employ a simple screw would find it helpful I’m sure, and this may also be true for screw-driven jigs for making dovetail joints.

The counter ( search for mechanical rotary counter on Ebay) cost me £12 – and would have been even cheaper if I had been prepared to wait for delivery from China – so it is not an expensive add-on for the jig. Besides full turns, the red wheel show 1/10ths of each turn, and should display 0 when the ‘clacker’ sounds. I don’t think that the red wheel will cause confusion, but if it does, it can easily be masked.

I will await comments on this project with interest, as I still am puzzled why someone cleverer than me hasn’t done this before.

-- Don, Somerset UK, http://www.donjohnson24.co.uk





7 comments so far

View StumpyNubs's profile

StumpyNubs

7483 posts in 2639 days


#1 posted 01-29-2017 05:26 PM

That’s very clever. It can be difficult to keep count with that type of jig. Good work!

-- Subscribe to "Stumpy Nubs Woodworking Journal"- One of the crafts' most unique publications: http://www.stumpynubs.com/

View Redoak49's profile

Redoak49

2904 posts in 1827 days


#2 posted 01-29-2017 05:37 PM

Excellent idea!

View helluvawreck's profile

helluvawreck

29192 posts in 2705 days


#3 posted 01-29-2017 06:16 PM

This seems like it would be a lot of help. Nice work.

helluvawreck aka Charles
http://woodworkingexpo.wordpress.com

-- If a man does not keep pace with his companions, perhaps it is because he hears a different drummer. Let him step to the music which he hears, however measured or far away. Henry David Thoreau

View woodbutcherbynight's profile

woodbutcherbynight

3647 posts in 2248 days


#4 posted 01-29-2017 09:50 PM

Good idea, looks great!!

-- Live to tell the stories, they sound better that way.

View htl's profile

htl

3169 posts in 998 days


#5 posted 01-30-2017 12:53 AM

HTL Here.
That’s just way too easy I wouldn’t want to use anything that made it that easy. LOL
Great idea and will be on the out look for one of these.

-- There's a hundred ways to do anything, alot depends on the tools at hand.

View kiefer's profile

kiefer

5580 posts in 2506 days


#6 posted 01-30-2017 03:33 PM

Great solution Don now what you need is a lockout so you can’t move the jig unless the count is at the right number .

Klaus

-- Kiefer https://www.youtube.com/user/woodkiefer1/videos

View Don Johnson's profile

Don Johnson

678 posts in 2619 days


#7 posted 01-30-2017 04:34 PM



Great solution Don now what you need is a lockout so you can t move the jig unless the count is at the right number .

Klaus

- kiefer

Hmmm – so one would need a database to store the number sequences, a keyboard with an input/editing system to create the sequences to be stored, a program for storing/running the sequences, an electro-mechanical system for preventing forward movement of the jig unless the current number of turns matches one in the current sequence and a digital counter to provide an indication of position – Oh! and something like a Raspberry Pie mini computer to organise everything. Whilst doing all the above, perhaps include a stepper motor to do the screw rotations automatically, and a chain drive system for actually moving the jig forwards and back.

Going on from there, should one add a small robot arm for loading the workpieces, and possibly a CNC system for cutting out box sides and ends?

You’ve got me all fired up on this, so watch out for another LJ post – I’ll try a get the whole thing finished by this weekend !!!!

-- Don, Somerset UK, http://www.donjohnson24.co.uk

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