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Student Instruments, Glue in the sound post


Dwight Brown
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Well, slightly less drastic than screws, and even less "permanent" than even velcro...what about this:

Attach a flange around the top and bottom of the post. Maybe using linen? If so, cost would be negligible.

The post can still be moved/reset/removed if required but can't fall over.

P.s. if anyone patents this idea, I get 10% royalties. ^_^

20210207_135429.jpg

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4 hours ago, Rue said:

Well, slightly less drastic than screws, and even less "permanent" than even velcro...what about this:

Attach a flange around the top and bottom of the post. Maybe using linen? If so, cost would be negligible.

The post can still be moved/reset/removed if required but can't fall over.

P.s. if anyone patents this idea, I get 10% royalties. ^_^

20210207_135429.jpg

I messed around with a similar concept a few years ago, but decided that it turned a simple, economical, and proven procedure into a complicated, expensive, and potentially destructive one, with no tonal improvement.  :)

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2 hours ago, Dwight Brown said:

This a Jurassic thread that has come back to haunt me!  The school instrument thing is something  I do not miss about my former life!  Those damn plywood 'cellos can shed them like nobodies business!

Cheers!

DLB

I call these zombie threads. I like the forums where threads are locked after 30 days of inactivity. If someone wants to return to the topic (not sure what the point was for this one...), they can link to the old thread as background, but perhaps reframe the topic according to the point they want to make. But I expect people here like things the way they are. :)

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36 minutes ago, caerolle said:

I call these zombie threads. I like the forums where threads are locked after 30 days of inactivity. If someone wants to return to the topic (not sure what the point was for this one...), they can link to the old thread as background, but perhaps reframe the topic according to the point they want to make. But I expect people here like things the way they are. :)

I agree! But then I give up and go with the flow.

At least Dwight is still here to respond (if he wants to!).

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Not complaining, just remembering the hell of trying to keep the posts up on those damn plywood cellos!  Still think I would have glued them to the back!  I don't miss that aspect of my 29 years as a school orchestra director on the edge of the world.

DLB

 

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So, is this a prevalent problem around the world??  I can imagine a simple solution for all posts except maybe it would not be desireable for the upper crust of instruments.

If I come up with a spruce  post/ accessory  design that once set and installed will not fall or move by itself, how many might I sell? sell price if produced  in volume likely in the order of $20

... worth researching?

 

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You can always just drive a thin nail down through the top into the post, like this.   I was going to adjust the post on this repair - it was in for something else - and decided the post was just fine where it was.

Please note that this was a sarcastic suggestion - don't do this.

IMG_1635.JPG

IMG_1636.JPG

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4 minutes ago, Brad H said:

You can always just drive a thin nail down through the top into the post,....

Yes you can but I would not dream of doing that on the worst of instruments.... If I did dream, it would be a nightmare!

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1 hour ago, Mat Roop said:

Yes you can but I would not dream of doing that on the worst of instruments.... If I did dream, it would be a nightmare!

I suppose my sarcastic post might lead some astray - I will amend it to make this clear.

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11 hours ago, Brad H said:

You can always just drive a thin nail down through the top into the post, like this.   I was going to adjust the post on this repair - it was in for something else - and decided the post was just fine where it was.

Please note that this was a sarcastic suggestion - don't do this.

IMG_1635.JPG

IMG_1636.JPG

Is the nail going down through the top or is it a pin coming up from the inside?

I want to do this correctly.

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Wow. Just, wow.

Posts are meant to be movable, adjustable, and replacable.

Violins are meant to be good enough to merit the trouble.

 

If a violin is so bad that you don't mind gluing or nailing the post in place, then go ahead.  Glue and nail that post in place.  Then finish the job by tossing the violin in the trash bin.

Or, paint the whole violin in a cute way, cut it open and install a litlle shelf.  Hang it on the wall as a cute display for small items.

 

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18 hours ago, Mat Roop said:

So, is this a prevalent problem around the world??  I can imagine a simple solution for all posts except maybe it would not be desireable for the upper crust of instruments.

If I come up with a spruce  post/ accessory  design that once set and installed will not fall or move by itself, how many might I sell? sell price if produced  in volume likely in the order of $20

... worth researching?

 

So no one has answered my question... Based on Dwight's frustrations... is this a general issue??? ... worth researching and developing a solution?

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4 hours ago, David Burgess said:

Yup. A removable screw would have allowed Brad to re-position the post, within a limited range, before putting the screw back in to re-secure it. ;)

 

The usual sound post is purposely made a little too long so that it can be wedged into place to securely hold it.  This puts the plate wood into a tension stress and its cross grain strength is real low so sound post cracks are a common problem.  To prevent this from happening I used to glue kraft paper disks on the inside of the top and back plates to strengthen the wood there.

If you made the sound post a little too short then a screw coming in from the outside would pull the top plate inward to meet the soundpost.   This would put an arched plate into a compression stress.  The compressive strength in the cross grain direction for wood is much stronger than in tension so this should greatly reduce the likelihood of sound post cracks.

This is the similar reasoning to why curved concrete dams have their convex side facing the water.  Concrete is much stronger in compression than tension.

The position of the screwed in sound post could be made adjustable by having the screw holes through the plates much larger than the screw diameter.  Large diameter washers could be used to spread the load over a large area and I suggest using spherical shaped screw heads and washers to accommodate the slopes of the plates.

A variation of this idea would be to make the soundpost way too short.  The screw could then be turned in or out to put the plates into various amounts of compressive stress.  This could change the plate vibration behavior and perhaps the sound character could be further adjusted.  This would be similar to these new screw adjustable sound posts but it would have an advantage of not having much risk of overdoing it and cracking the plates.

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4 hours ago, David Beard said:

Wow. Just, wow

I haven't read the entire thread but the comments I have seen have all been facetious.

 

1 hour ago, Marty Kasprzyk said:

Large diameter washers could be used to spread the load over a large area and I suggest using spherical shaped screw heads and washers to accommodate the slopes of the plates.

Titanium washers, I assume to lighten the load...

Another solution which derives from a similar- but much more misguided -  principle  as the integral bass bar, would be to carve the post from each plate.   The half-height posts from each plate - one of spruce and one of maple - would then be joined together in some fashion as the top was glued on.

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