Anyone Ever Shortened a Shahe DRO Scale?

[awemawson]

I'm fitting a DRO to my Thicknesser  which is part of the Dominion Woodworker - it doesn't need to be anything too precise - nearest 32nd of an inch is fine !

I've bought (Alliexpress) a Shahe 12" scale - I only need 9" of travel and although not essential to shorten it, it would make mounting a tad easier. It's going to be magnetically attached, and to preset the reading the plan is to thickness a bit of wood, then slide the mounting magnets until the reading corresponds with the previously thicknessed wood.

It looks as though the scale part is made by the yard and could just be sliced off where needed, but is this the case 

. . . anyone actually know for sure ?

[John Rudd]

They are standard scales with an aluminium substrate....just cut to length and all will be well in the world...

Done it several times and no one died...

[awemawson]

Thanks John, that's reassuring to hear 


 

[PekkaNF]

Not sure about that one, but pretty sure it's capacitive scale, most of them are incremental (no position information is coded on them, no home-position or anything) and there is a metal base, which has a narow groove to house PCB, that has an etched pattern (picture above). Top of that is protective tape.

Nothing is harmed when it is cut cleanly. Pretty much only danger is related to PCB/tape entagling to saw blade, I would leave some extra and cut carefully trough the top layer.

There are some exotic models, like both scale and reader are powered (you see cable connected into scale too) and/or absolute postion encoding....like these:
http://www.kappasense.com/kappasense-technology/

Many uncommon flavors, but the cheap ones are all basically the same construction than cheap verniers (picture on the top).

Pekka

[awemawson]

I've not actually cut the scale yet, however I bent up a crude bracket to join the 'traveller' sensing head to the Thicknesser thickness indicator using a rare earth magnet - just proof of concept.

Seems to work remarkably well - the readings in the photograph of the DRO and the digital vernier are genuine - 1 thou apart ! but the eagle eyed will notice that the digital vernier is on 'hold' as I couldn't keep it in contact AND take a photo

Quite pleasing. I think that I will now 3D print an adaptor that will bolt to the sensing head, and present the 15 mm rare earth magnet pressed into a hole and angled at the required 45 degrees to match the pointer on the Thicknesser

(The reason for shortening the scale is to allow more room to slide it on it's magnetic mountings to allow me to preset the DRO)

[awemawson]

Encouraged by the above I decided to draw up an adaptor in Fusion 360 and 3D print it. I decided to have it entirely behind the sensor head and space the scale off on pillars to make room.

Worked out remarkably well - made up some 20 mm high spacers out of hex brass, tapped M3 one end and M4 the other, only because I didn't have M3 countersunk any longer than 20 mm and the magnets have a 3 mm hole.

As the magnet goes on to a 45 degree slope the exact pillar spacing is less critical - the magnet sticks on where it needs to 'up the slope' but in practise is pretty near the middle 

Next job - shorten that scale 

[awemawson]

So no more procrastinating - get on with it !

I carefully measured up, and came to the conclusion that if I shortened the scale by 60 mm it would give me sufficient wiggle room to pre-set the DRO but still allow the full 9" of Thicknesser travel unimpeded.

So a simple job of unbolting the end mount, clamp it in the vice, attack it with a hack saw, make it pretty with a file, and re-fit the end mount. All unexciting and nothing to be concerned about. As others have said, the scale comprises a PCB supported by an aluminium beam to which it is bonded.

I tried to get a picture of the cross section, but it isn't the best quality photo.


So the procedure is:

a/ Fix the scale to the cast iron body of the machine with super magnets

b/ Slide the sensor head down until it's  attached magnet contacts the original machine pointer and firmly fixes both together

c/ Adjust the thickness wheel to give as near to zero thickness as possible

d/ Zero the DRO

e/ Adjust the thickness wheel to approximately the desired thickness

f/ Plane a bit of timber at this setting and measure it

g/ Slide the fixing magnets and hence the scale to give the same reading

h/ Do a trial planing to check the results.

Now with this particular DRO the setting will be retained even when powered off, so as long as you remember NOT to press the zero button and nothing else is disturbed there is no need to go through the above procedure - the machine is ready to use 

[WeldingRod]

I've cut those down too, even going so far as to peel off the working bit and graft it into a lathe cross slide!
I have also cut down a GLASS scale, but that's a lot more fiddly!

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