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ClefLover

Extremely stubborn blocks!!

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I am having a heck of time removing a cello top.  The top and bottom block area will not budge.  I even pushed my heat a little hot and scorched a tiny bit of varnish!  Any tips!?

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Just now, Thomas Coleman said:

Make sure the varnish is not spirit!

Or work very carefully :) maybe use a small syringe?

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2 hours ago, ClefLover said:

I am having a heck of time removing a cello top.  The top and bottom block area will not budge.  I even pushed my heat a little hot and scorched a tiny bit of varnish!  Any tips!?

 

The best way is normally to stump off down to the pub, and try again tomorrow

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35 minutes ago, jacobsaunders said:

 

 

The best way is normally to stump off down to the pub, and try again tomorrow

 

Yep,that will probably work.

Best not to try it after coming back from the pub though.

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14 minutes ago, Delabo said:

Yep,that will probably work.

Best not to try it after coming back from the pub though.

That might actually give you the courage it takes to make one clean blow to your knife/spatula - just hard enough :)

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4 hours ago, Thomas Coleman said:

Make sure the varnish is not spirit!

There are plenty of oil varnishes that are more than sensitive to alcohol.  To make things more confusing there are coatings that were spirit that are now not very alcohol soluble.  

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My question about heating the opening knife was because I think that might reactivate the glue and make things more difficult. Glue releases best when very dry.

I agree with Chung that the best bet is to use a very long tool like a baker's cake frosting knife so you can come at the joint from inside the cello if needed. Check for grain runout first then knock off any glue beads to make sure your knife is exactly on the joint and give the knife  a brisk tap with a mallet or small hammer to break the glue. Once the bottom is off there is a tool described in the Weishaar book that can reach the inside of the top block. They  have a description of how to use it and also recommend a percussive shock to open the joint.

 

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13 minutes ago, nathan slobodkin said:

My question about heating the opening knife was because I think that might reactivate the glue and make things more difficult. Glue releases best when very dry.

I agree with Chung that the best bet is to use a very long tool like a baker's cake frosting knife so you can come at the joint from inside the cello if needed. Check for grain runout first then knock off any glue beads to make sure your knife is exactly on the joint and give the knife  a brisk tap with a mallet or small hammer to break the glue. Once the bottom is off there is a tool described in the Weishaar book that can reach the inside of the top block. They  have a description of how to use it and also recommend a percussive shock to open the joint.

 

I’m not sure if I made up the heated knife thing, or if it was once recommended to me, but everytime I give it a try I end up slightly affecting the varnish in a small area.  I did give one more whirl yesterday evening and finally got the end block portion loose.  I’m sure I’ll have a few questions as the repair is for a partially unglued bass bar.

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Just now, nathan slobodkin said:

One more thought on this although not helpful in this case is when building instruments I always bevel the top surface of the upper and lower blocks to guide any future repairman's knife into the joint.

Thank you Nathan - will incorporate.

cheers edi

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25 minutes ago, ClefLover said:

I’m not sure if I made up the heated knife thing, or if it was once recommended to me, but everytime I give it a try I end up slightly affecting the varnish in a small area.  I did give one more whirl yesterday evening and finally got the end block portion loose.  I’m sure I’ll have a few questions as the repair is for a partially unglued bass bar.

While heat can release glues such as Titebond and epoxy, I haven't found it helpful with hide glue.

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26 minutes ago, nathan slobodkin said:

...when building instruments I always bevel the top surface of the upper and lower blocks to guide any future repairman's knife into the joint.

Do you consider it appropriate to bevel the original blocks of an old instrument you have apart for repair before regluing the top?  If you consider it inappropriate, how about if the repair includes replacing the blocks?   (I am facing this situation right now.)

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28 minutes ago, FiddleDoug said:

Hide glue doesn't melt!!! You must be thinking of PVA glues.

I’m not sure why I try some heat with stubborn tops, again, I think my imagination mislead me with the thinking that hide glue starts to melt at 140 degrees [with water].

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3 hours ago, ClefLover said:

I’m not sure why I try some heat with stubborn tops, again, I think my imagination mislead me with the thinking that hide glue starts to melt at 140 degrees [with water].

That's as a gel, dissolved in water. Once it's dry, it won't melt until it's ready to char and burn.

http://www.frets.com/FretsPages/Luthier/Data/Materials/GlueTest/gluetest.html

 

 

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