Thread: A simple compass

Originally Posted by derekcohen

Tell us more about the construction.

Thanks Derek, there's not much more to add really but I will give it a go.

Like I said the legs are made from 3 x 25 mm Ally SHS and 19 mm ally round tube.
These two sizes of tubing are really made to work together as the 19 fits perfectly inside the 25 and I have used these together quite a bit - for example it is easy to firmly join two pieces of 25 at right angles to each other using a short piece of 19 and a bolt - I used this extensively when making my Macro photography stand - I should take some pics of how I do this next time I make such a join.

I bought 2 x 6 m lengths of the 25 mm SHS to make some full length tie down rails for inside my van so I had heaps left over. The 19 mm tube was left over from an anti-sag device for my 60" chainsaw bar.

The SHS, as was all the ally, was cut on a WW Table saw with a special ally cutting blade. The 25 mm leg was cut lengthways with a ww tapering jig. The rest was drilled with a DP, and filed by hand or using a belt sander.


The hinge is a short piece of 8 mm brass rod tapped at both ends. The main Hinge recess (area shown bounded in red) was hogged out using the table saw and then filed to fit.

One of the hardest things was drilling the 3/16" countersink on the otherside of A - remember the 19 mm tube has to fit inside the 25 mm tube so none of the head can sit above of the surface. I did this using an old dremel stone bit that I shaped to fit the countersink profile using a devil stone. The stone bit was short enough to be able to fit in from the other side and then I attached the bit into a DP and on slow speed and using meths as a lube I let it grind the countersink profile while applying a light downward pressure on the ally. It's not all that precise but it worked.

The marker holder detail is a follows

The material is 12 mm ally plate. It was cut to size using a table saw with an ally cutting blade! How do I do this on such a small piece? I hold the piece in a clamp and hold the clamp and free hand cut it taking it really slowly and using hard wax as a lube . Please note this is done wearing a full face shield, ear muffs and a long sleeved shirt as the ally shards are nasty. A belt sander was then uses to shape the rounded edge along the long angled side.

Then I drilled the long angled 9/16" hole at D - This is pretty nerve wracking as it is done at an angle and it is quite hard to start such a hole - but not if you use a forstner bit to start it off (6 mm) and lots of Meths lube.

A & B are tapped holes for 3/16 countersunk screws

C is a hole tapped to hold a 1/4" piece of all-thread with a slot cut in one end to act as a driving point. The 1/4" goes all the way through to the knurled knob that can ride out on the thread and contact the marker. The square hole for the knob was hogged out using a 1/4" drill at the corners and then a 10 mm forstner bit. Then filed but hand. You can see I messed it up as it is not symmetrical about the knob.

Finally the cam lock.

The cam itself is also made from 12 mm ally plate. Cut to approx size using a table saw as per the marker holder. Then 1/4" holes are drilled at A and B. One could also be drilled at C. After that it's join the holes as best one can with a bandsaw and full bore on a belt sander and eventually a Dremel to do the inside curved parts of the cam. It takes some time but I like doing it so I don't care about the time.

The locking mechanism is via a A 1.5" long 5/32 countersunk screw riding in a long keyhole slot in the tubular leg. The countersunk screw has a 8 mm long, 8 mm diam brass lug tapped and threaded and silver soldered at the head of the screw. The lug is then filed into an inverted T-profile so the leg of the T locks into the slot to stop the screw from turning when the cam is adjusted. The screw head and T-lug fit neatly through the keyhole that can just be seen in the tube. To help the locking mechanism slide along the leg a curved whiteHDPE block is used.

Cutting the long keyhole slot was a PITA. This would be dead easy with a metal working mill but I was determined to do this without using a mill so I drilled out the line using a 1/8" bit and then filed it by hand. The problem was getting the line straight - which it isn't but it's straight enough for it to work.

Clear as mud - I can disassemble the locking mechanism and take more photos if anyone is interested.

FInish is just brushed with a scouring pad wheel but it could do with a proper sanding to remove all the scratches first!

Very nice work BobL.

Carefully thought out and precisely executed.

Not being a "metal person" - I have heard of issues regarding aluminium and brass. Have you done anything to overcome this or is it not necessary in the shed environment?

Regards,
Bob

Originally Posted by Bob38S

Very nice work BobL.
Carefully thought out and precisely executed.
Not being a "metal person" - I have heard of issues regarding aluminium and brass. Have you done anything to overcome this or is it not necessary in the shed environment?

I can be a problem outside but is less so inside a shed.

Where practical I have put a plastic washer between the ally and the brass. I need to replace the brass washer that sits under the cam with a gold passivated one. Using a thin coating of light machine oil on the brass threads that pass thru ally seems to reduce any corrosive effects. If it was an every day use tool I would have done things differently but I will be lucky to use this every few months.

Here's a bit more brass'n'ally work. These are another type of cam lock I made for my chainsaw mill.


Since the mill spends some time outside I do see some slight corrosion effects between the brass and ally. I did originally have a white Polypropylene (PP) strip (as shown in the photo) between the brass and the ally, but the steel cam wore the PP away and it ended up splitting too quickly. I then tried Polycabonate without success. I have since changed these contact points to a thin ally strip with gold passivated washers between the brass and ally.

Thanks for the info - keep the sharing of the projects coming - it's much appreciated.

I've been curious about this "problem" for a while as I have a number of bits and pieces from "Veritas" and they use brass with aluminium. I have assumed, rightly or wrongly that they have managed to use the dissimilar metals together because the aluminium appears to be anodised.

Regards,
Bob

I like the workmanship it looks professional. I have a staedler set nothing unique but they are good. Yours looks and I bet feels unique. Did you do the bending on the sheet metal yourself. Once again professonal.

Originally Posted by peteandoreen1

I like the workmanship it looks professional. I have a staedler set nothing unique but they are good. Yours looks and I bet feels unique. Did you do the bending on the sheet metal yourself. Once again professonal.

Cheers P&D, There was no bending involved. The rectangular leg was cut on table saw on a taper cutting jig from a length of SHS ally.