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tango

Cello centre joint. Preferred method?

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Hi all

After two years of postponement I began a cello.

At the present  time I only made 10 violins and 3 violas.

Some top plates were rubbed and some clampled as all my back plates being this backs the most difficult task.

1)Is there any trick for planning centre joint in the case of a cello? 
2)Somebody used a shooting board for cellos back?
3)Is any method preferred to other?

For the moment I am thinking to work as always but I am a little affraid :unsure:

Regards

Tango

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51 minutes ago, tango said:

Cello centre joint. Preferred method?

[Examines several student cellos.]  Make it a one-piece.  Just use a larger piece of maple-veneer plywood.  [Hurriedly exits the thread while keeping to cover.]  :ph34r:  ;)  :lol:

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1 hour ago, tango said:

Hi all

After two years of postponement I began a cello.

At the present  time I only made 10 violins and 3 violas.

Some top plates were rubbed and some clampled as all my back plates being this backs the most difficult task.

1)Is there any trick for planning centre joint in the case of a cello? 
2)Somebody used a shooting board for cellos back?
3)Is any method preferred to other?

For the moment I am thinking to work as always but I am a little affraid :unsure:

Regards

Tango

Here is the deal with seams, to me it does not matter how you get there, just that you do,and "there" in this case is a "no light seep seam", those with confidence in their plane system will use that,others will "cheat" and use a power joiner, and which ever you use,just makes sure it's tight before you try to glue

If you are really worried about it and just want to move on with the project, you could find a local cabinet builder who has a power plane and offer a small amount of money to him for running the two edges

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At the summer workshop I started using chalk on center joints as a tool to show people where problems were, and got to really like the feedback. Now I do as perfect of a job as I can, and then check it with chalk. It's never quite as good as one thinks, even when all of the external checks are perfect, but the chalk shows what's really happening. Usually a few scrapes with a scraper moves the joint to perfection, and I've never had such perfect joints.

The way to test with chalk is to chalk one piece held in the vise, then lay the other on it starting by holding one end down tightly, maintaining that pressure, and lowering the whole piece, like an old-fashioned movie sound clapper, but gently. Don't push anywhere but the one end, and use that hand to slide the upper piece back and forth a little.

I'm also scoring the joint surfaces, old Cremonese style. I think what this does is prevent all of the glue from being squeezed out when the pieces are slid together, which is something i sometimes had problems with in the past

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15 minutes ago, Michael Darnton said:

At the summer workshop I started using chalk on center joints as a tool to show people where problems were, and got to really like the feedback. Now I do as perfect of a job as I can, and then check it with chalk. It's never quite as good as one thinks, even when all of the external checks are perfect, but the chalk shows what's really happening.

Yup, chalk fitting can reveal things which other methods can't.

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19 hours ago, Michael Darnton said:

I'm also scoring the joint surfaces, old Cremonese style. 

Have you seen evidence of this from certain makers?  It must be a light scoring or else it would show on the seam, right?

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Hi

Violadeamore. :D:D:D
 

Jezzupe. I guess the power plane vibrate so much. It would be ok for the first aproach . Isn´t it?
 

Michael. I thought I was the only one that chalked the back centre joint. Always work a lot between curled maple becauuse a very little light is there (without clamps)
 

David. I found an old (2008) photo of your gluing system for cello´s back using glued wedges. I like that.

Thanks all for advices an information

Tango

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I haven't joined cello wedges, but have jointed fairly large pieces of timber.

However if I was, rather than using a shooting board, I would clamp the wedge to the bench top with a mdf spacer under it. If the bench top was flat enough it could be used as the running surface for the plane on its side.

Make sure that the wedge does not rock when laid on the mdf because clamping pressure could twist the wedge. The best thing to do would be to find where the wedge makes contact with the mdf and clamp at those places.

I've found a large, low-angle, bevel-up plane works better than a Stanley style bevel-down because it is easier to hold.

You could either have the planing edge facing out or facing in, which would mean having to reach across the wedge to use the plane, but it might more comfortable.

 

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I've joined only a few cello tops and backs, first just by doing a simple rub joint (no clamps used), and then trying out a clamping method that I believe was shared by David Burgess (if my memory serves me well?):

Basically, by staying outside of your marked out outline you can cut oversized 'button' extensions on both sides of the center joint, which can be clamped with smaller sized clamps. To clamp the center of the plates, glue short but wide tower cleats on either side of the seam - tall enough that the clamp can grab on to it, but short enough to discourage the joint from pivoting and opening up the non clamped side. I made mine pretty wide to maximize the glue surface area holding the cleat because I was paranoid the clamp might rip it off and cause a large chip out. Its been awhile, but I think I only glued these tower cleats to the inside of the plate because I was concerned about 'glue ghosts' showing up when I varnished - but I'm certain I did multiple checks to ensure the plates didn't pivot towards the clamp when pressure was applied. 

For joining cello plates I feel it's necessary that I size the joint / pre coat with hide glue for some reason (never do this on my violins and violas). I make my last couple passes with my plane after the surface has dried, just in case the moisture has distorted the surface and compromised the joint. Anyone else do this?

Finally, if you are going to follow Mr. Darton's method for any center joint, I'm sure he'll tell you to do your best to ensure that the plate half you have clamped in the vise is true, and not distorted in some way - or, if it is irreparably warped, clamp it once and fit and glue the joint without moving it ever again. One of my first center joints in school would flex every time I clamped the plate in the vise, causing the joint to distort every time the plate half was released and returned to its relaxed position - it really messed with my head as a novice :) . 

Oh, and I second reading Mr. Slobodkin's posts (on all matters really, but especially concerning cellos) - I don't think he is kidding when he says hundreds made. 

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