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Old 1st November 2012, 03:00 PM   #131
abone is offline abone  Canada
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Thanks for this. Is that the length you go with? 9mm long enough?
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Old 2nd November 2012, 12:01 AM   #132
abone is offline abone  Canada
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Thanks for this. Is that the length you go with? 9mm long enough?
I meant 90mm long enough?
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Old 2nd November 2012, 12:32 AM   #133
Rush is offline Rush  United States
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Quote:
Originally Posted by abone View Post
I meant 90mm long enough?
Use a forstner bit to adjust the pad the bolt head rests on. Put a stop on the drill press so they are all the same length.
I got mine from McMaster Carr also.

Rush
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Old 2nd November 2012, 01:55 AM   #134
Bon is offline Bon  Australia
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Quote:
Originally Posted by abone View Post
I meant 90mm long enough?
I use 90 mm countersunk in the base. I like to clamp the SP10 through the full thickness of the resin plinth. This allows the bearing to be pulled down in contact with a bearing drain, which is 6 mm of sheet lead in my plinth.
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"Moderation is a fatal thing. Nothing succeeds like excess." Oscar Wilde.
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Old 2nd November 2012, 04:32 AM   #135
abone is offline abone  Canada
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Thanks guys, this is helpful. I was under the delusion my plinth had to be a minimum of 5" (127mm) so was resigned to using threaded rod cut to fit. I ordered the 90mm bolts from McMaster Carr today and will reduce the height of the plinth accordingly.
Another question regarding constructing with Baltic Birch - is it critical what thickness each layer is? Should I use 1/2" vs 3/4" or doesn't it matter?
And is there a preferred glue to use. I thought I read somewhere a poly wood glue is best but damn if I can find that reference again.
Thanks,
Andy

Last edited by abone; 2nd November 2012 at 04:36 AM.
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Old 2nd November 2012, 07:44 AM   #136
Bon is offline Bon  Australia
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Quote:
Originally Posted by abone View Post
I ordered the 90mm bolts from McMaster Carr today and will reduce the height of the plinth accordingly.
One more thing. The bolt for the front left needs to be 5 mm longer than the other four. For some reason the thread is set higher up in the frame casting. You could alternatively countersink the hole 5 mm deeper.

Quote:
Originally Posted by abone View Post
Another question regarding constructing with Baltic Birch - is it critical what thickness each layer is? Should I use 1/2" vs 3/4" or doesn't it matter?
And is there a preferred glue to use. I thought I read somewhere a poly wood glue is best but damn if I can find that reference again.
I have never constructed a birch ply plinth, but when I was comparing constrained layer damping materials for speaker enclosures, I found PVA glue tested badly compared to other damping layers like glazing silicone. I'm not sure how BB ply is supposed to work in this application. Is it the natural resins in the timber or the glue used in the laminations? Don't depend on the PVA tp provide the damping required for an effective constrained layer.
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Old 2nd November 2012, 12:46 PM   #137
Rush is offline Rush  United States
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Originally Posted by Rush View Post
Use a forstner bit to adjust the pad the bolt head rests on. Put a stop on the drill press so they are all the same length.
I got mine from McMaster Carr also.

Rush
If you don't know what a Forstner bit is:
"This 1 5/16" Forstner bit features a 3/8" shank and is machined from high quality carbon steel. May be used in a drill press and with extra care in a hand drill. These bits cut holes with clean sides and flat bottoms and will not burn if you stay within the recommended speed as stated on the box. The bit has a saw tooth rim to reduce heat and to minimize larger bits' tendency to burn. Overall bit length 3 1/2"."

1 5/16" - Forstner Bit-Traditional Woodworker

Rush
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Old 3rd November 2012, 04:02 AM   #138
abone is offline abone  Canada
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I'll make sure I use one of those bits. I'm having the cutting and routering done by a cabinet maker but I'm doing all the legwork as far as plans, materials etc.
I found the reference to PL glue over at audiokarma. This is the stuff someone said to use with BB ply on a plinth.
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Old 27th April 2013, 08:18 PM   #139
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Default Plinth materials....continued

It may appear I'm dragging my feet on this project, and this is true. But I continue to refine my ideas about plinth architecture. I have no sketches that I'm willing to share with the public domain....yet. That will be coming within the next month. Fwiw, I have determined the overall shape and layout. It is now a matter of working out the numerous details.

One of those details is plinth materials. We've already discussed bentonite filled isophthalic resin as a 'castable' material with excellent damping properties as well as having very good tensile and sheer strength properties.

Another material candidate has been brought to my attention. NAD-11. There is a company in Washington state that produces this. Pyrotek. They are located in Spokane The material is described as a high density cement board reinforced with inorganic fibers.

I understand that Cats Squirrel has already been supplied with a sample but I don't yet see any damping property test results on his website. Meanwhile, the material is claimed to have:
  • a density of 109 lb per cu ft.
    flexural strength of 4640 lb/square inch
    Dialectic strength of 2.9 KV/mm
    excellent machinability
    etc.

Now if we just knew its damping properties...

meantime I need to make a test sample out of the isophthalic resin with kitty litter.

soon.
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Old 28th April 2013, 11:52 AM   #140
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the damping factor of the Pyrotek sample (6mm thickness) is on the web site, it is 0.376 at 100 Hz, the 20mm thick sample measured 0.395 at 340Hz.

HTH
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