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1970s Design Indulgence

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Graham Slee View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 03 Jun 2023 at 8:17am
Found a more affordable nutsert kit at shopfer...



Edited by Graham Slee - 03 Jun 2023 at 8:20am
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Post Options Post Options   Thanks (2) Thanks(2)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jun 2023 at 3:30pm
Drat! Setback = thickness + bend radius. How could it be any different?

So, I'm pleased this is soft metal and the pan brake is really tough...

So far I found it impossible to set the setback with an engineers rule. What is required is some sort of thickness gauge.

Double drat! Obviously with the apron raised and the fingers clamping the correct material (but set under a little), it requires an offcut of the same material plus the bend thickness, from the bending tables, and the setback adjusted so they're only just nipped.

So where do I get a 0.6mm thickness? Feeler gauges! Except that I gave up car servicing ages ago and I have a diesel.

Bezos to the rescue (triple drat). Hopefully the Draper feeler gauge set will arrive by 1pm tomorrow.

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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jun 2023 at 7:16pm
Impatient as always, I found sufficient shim material to make 1.85mm and set the setback against it.

I scribed a line 4.76mm off the Vernier from the 1.2mm 1050 aluminium offcut edge.

I placed it by sight under the brake's fingers, clamped it firm and hoped for the best.

I rotated the apron about 3 degrees over 90 on the Trend magnetic angle gauge to ensure a 90 degree bend. It turned out to be about 93 degrees outside angle and so I'll not over-rotate in future!

After coaxing it back on the edge of my desk, I then measured the internal and external fold dimensions.

It was over at 5.15mm. 5.00mm intended.

external fold measurement

Internal, it was 4.00mm. 3.8mm intended.

internal fold measurement

My measurement accuracy must therefore be in the order of 0.05mm (2 thou).

The internal measurement used the Vernier's step measuring faces which is round the back.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jun 2023 at 9:15am
Quite difficult working with hobby machinery that isn't precision. I guess their excuse is that it's only for hobbyists who won't care or have a clue what precision is.

I formed the first mounting pan this morning.

formed pan

1. Guillotine the RS aluminium 1050 200 x 300 sheet to 200 x 210.

The tray is only 189mm deep, so I had to use a steel rule beneath the stock up tight to the end of the tray, to clamp the stock at 210.

The other side of the tray is 188.5 deep...

The rule under the stock is therefore inaccurate.

Enter my new Mitutoyo old school Vernier gauge. Set to the offcut hanging out the back, that should be 90mm if RS cut the stock correctly, I could use the shoulder measurement to adjust for 90mm. I did, and then found the stock was not exactly square to the tray side. Difficult to tell if that's the guillotine or the RS stock.

Clamped with the aid of a 9mm MDF offcut using two Kreg Automaxx face clamps, the cut was made, and the piece found to be 200 x 210 just about exact.

Unfortunately out of square by about 0.5mm per 100mm says it's RS at fault.

2. Scribe the 4.76 in from all four edges. Punch corner bend relief holes on the WP82 at 3/16 (4.8mm). That caused some distortion of the corners as there is only 2.4mm of "meat" left. I should have used the 1/8 (3.2mm) punch I suppose.

3. Set the workpiece in the pan brake and adjust, readjust, repeat, etc, until the scribed line just disappears under the near clamped fingers.

Fully clamp and lift the apron to form the fold at 90 degrees. Checked with the Trend angle gauge.

Repeat another three times.

4. pull the folded corners flush with the WP82 3/16 die, and punch the four corner mounting holes.

5. Check!

Across corners the corner mounting holes were the same distance in both diagonals. Tick!

Measure the folded flange heights. Not so good! Not completely parallel. Measured 5.35mm to 5.60 at several points around the pan.

Sat the 75mm tall heatsink on it in the MDF prototype case and with a straight edge, it just misses the lid ledge height by a tiny fraction.

I wanted it 1mm, but it's much less. The woodwork machinery and its operator produce greater accuracy.

heatsink stood on pan

I'll try again later as I require two pans.

I will add that the folds result in the desired rigidity of the pan.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote peterb Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jun 2023 at 9:44am
Don't beat yourself up too much. In the sheet metal shop we had an expected finish tolerance from a CNC Punch Press and CNC Folding machines was 0.5mm.  Smile
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Dual 505-1, Cyrus CD T, DIY 80W MosFet amp and PreAmp, 2xKEF 103.2
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jun 2023 at 9:47pm
Still the flanges are 5.35 - 5.55 mm, so it has to be the setback adjustment, and I will have to make yet another base pan.

With such small increments however, the corner holes (die set tight into the corners) are probably within 0.5mm overall, and that gives confidence that a template for the wood base should always line up.

So the next job is to arrange the parts on the base pans and draw up the hole centres.

I will have to precision drill into the heatsink vertically and thread the holes M4 to mount it. I will also add an RS bracket midships as a stay, just in case. Then to arrange the power transistor pairs such that there is space in the middle so the transistors nearest the centre don't overheat each other much. 
Plenty of drilling a tapping to do, but I've had to do it before, and using high speed steel taps rather than carbon steel, it should not be a problem for a DIYer equipped with a decent drill press and a modicum of mechanical sense.

And after the power supply base pan is done, then I have to get the layout right on that Japanese AT-40W SRBP board I bought.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jun 2023 at 8:58pm
Real wood. We chose solid ash for its sustainability. This is a pre-glue-up image with just the switch hole in the otherwise blank front panel, to be cut. Once glued up, the sharp lines will be rounded over, and the frame will be sanded and given a natural waxed finish.

milled and machined solid ash to make the front, back and sides of the amplifier

The background is the bed and custom built fence of the jointer/thicknesser machine. The manufacturer's fence wasn't reliable enough to do 90 degree corners repeatably.

Cutting the mitres was also challenging in that the mitre gauge wobbled. An exact 90 degree mitre gauge was made from an offcut of ash for the runner and a piece of MDF screwed to it while clamped to the saw table fence with a 90 degree gauge. All surfaces including the saw blade were waxed so the only friction was between the blade and workpiece, resulting in accurate 44.7 degree mitres to give gap-free corners.



Edited by Graham Slee - 09 Jun 2023 at 8:59pm
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