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Old 25th June 2012, 09:05 PM   #1
kctess5 is offline kctess5  United States
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Default Cut sheet issues

Let me preface this by saying that these are not criticisms, the designers of the enclosures I refer to were kind enough to design the boxes and provide support for them free of charge, so its hard to hold minor issues against them. This is just advice for future builders...

I've now built two enclosures from the community site plans including the Classic golden ratio Mar-Ken10.2 and the now archived Aikos from Frugal Horn and in both of them there were a few issues with the designs and/or cut sheets.

I just built the Mar-Ken10.2 and here's a few things I noticed:
1) On the cut sheet the baffle is too small. If you look at the plans the 14 27/32 dimension is not the entire baffle. The correct dimension for the cut sheet is 15 19/32
2) The sides are too short. If you actually all of the dimensions it comes to 17 11/16 but on the dimensions and cut sheet it says 17 9/16.
3) The horizontal port slat is too long. It should be 5 3/16 instead of 5 9/32

I think that was it but I might have missed something.

On the Aikos there were a few things that I notified Scott about but I can't remember off the top of my head. It was tricky because both the cut sheet and dimensioned drawing were wrong in a few places and I had to figure out which one was correct. At one point I used dial calipers to measure the actual picture and scaled it up to figure out the correct dimension.

If I had to guess I'd say that these problems come from the conversion to metric to english. My sample size is admittedly small but given that both I have made have had a couple of issues I wouldn't be surprised if others do as well. I think if you measured and cut everything according the metric dimensions there would be less problems. Unluckily my saw doesn't give me that option.

The moral of the story is just double check everything before you cut to avoid problems. I would suggest redrawing it on a separate paper and redimension everything using the overall dimension, internal dimensions, and material thickness to find places where lengths are not quite right and to just double check everything.

Once again I'm not trying to disrespect the designers, I'd say that this sort of checking is a small price to pay for a free design

Happy hunting
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Old 25th June 2012, 09:34 PM   #2
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I don't trust any drawings, even my own.

I usually do a full scale layout actually on the sheet of material I'm using, that way I can double check things like thickness of material, depth of rebates and suchlike before I cut.
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Old 25th June 2012, 09:48 PM   #3
kctess5 is offline kctess5  United States
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Quote:
I usually do a full scale layout actually on the sheet of material I'm using, that way I can double check things like thickness of material, depth of rebates and suchlike before I cut.
Thats a great idea, I may have to start doing that...
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Old 25th June 2012, 10:21 PM   #4
chrisb is offline chrisb  Canada
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I've probably built more enclosures from among the literally hundreds of Dave's enclosure drawings over the years than anyone, and you're quite right about having to double check the dimensions. Not the least of the explanations for errors is the conversion to and fro between imperial and metric, and the default material thicknesses.

As I'm often able to take advantage of in house CNC for machining of parts as simple as a single round rebated driver cut out to the side panels for the FH3 flat packs, I always redraw them in my own little steam powered CAD program (AutoSketch 1995 - "now runs in both Windows 3.1 and 95" ) to verify sheet layout for multiple pair batches ( which can be quite different from a single pair) as well as to produce DXF files for export to CAM (AutoCAD>Drillmate>Aspan>Morbidelli/Xilog)

All of our big production machines are either European ( Morbidelli CNC, IDM edgebander) or have control consoles easily be calibrated in metric ( Giben beam-saw), and all the table saws have both on the Biesemeyer rip fence rails.
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Last edited by chrisb; 25th June 2012 at 10:36 PM.
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Old 25th June 2012, 10:42 PM   #5
puppet is offline puppet  United States
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Years ago we used to lay everything out on a rod (square 1x1 stick basically). Each edge holds the layout for width, depth, height of your case (or whatever). Part dimensions can be compared directly to the rod.
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Old 26th June 2012, 09:16 PM   #6
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Corey,

Thanx for unearthing the bug. I went thru the drawings, and i did draw the baffle 18mm short on cut-sheet (taking the value from the dimension with the wrong take-off point).

That was the only inconsistancy i could find in the drawings. I have updated them, and added a few more dimensions.

It should be noted that plans in metric unit material (ie 15/18mm) will usually be rationalized to mm (all integer units) -- these exemplified by p10-hifi plans, and plans in 3/4" rationalized to imperial (the 1st off of any Woden plans, 1/8"). The conversion of units in the drawings is done by the CAD software. So if you see 10ths of a mm, or 16ths or 32nds of an inch, the drawing is likely native to the other units. Due to angles it may not be possible to get "exact" units. If you see both tenths of mm and 32nd inches, the drawinghas not been rationalized.

One comment on the dimension conversion by my CAD program. There is a bug, where sometimes, when i'm switching units around, that the secondary imperial units are rounded to the nearest 1/2" instead of the 32nd specifed. If you run into a drawing with the finest imperial dimension is a 1/2" contact me immediately, it is almost for sure an instance of this bug.

There are other ways in which dimensions are off. I have 1000s of drawings and rarely do i need to start from scratch anymore, taking an existing drawing and modifying it. It is easy to miss re-snapping a dimension leader to the right feature. A close look at a drawing will usually show these up.

And then there are just silly mistakes.

Further to this is that, for instance, 18mm material is rarely exactly 18mm. A material spec sheet recently posted by another member illustrates. The sheet was for 3/4" BB. The spec was 18mm +/- 0.4mm (3/4" ~19.1 mm). Further we have found material where thickness of a sheet varies. The worst case i've seen of this was the 5/8" chipboard we found when we took the side off of a commercial horn It was driving Chris crazy, until i noted that the material was 15 mm +/- 2mm. We also got bitten on the 1st batch of FH1, Chris had to go back and trim one edge of some internal pieces so they would fit into the rebate.

What this means, is that with any plans, one must adjust for the actual material thickness that you buy. I suspect that this is and 64ths building up, were where Corey observed other dimensional issues with his build.

Posting the update caused a cascade of stuff related to my websites and you can find the new file on frugal-phile.com.

A more comprehensive note is here:
Planet10-hifi web site will be a mess...

dave
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