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 Post subject: Vacuum bridge clamping
PostPosted: Mon Jun 07, 2021 10:29 pm 
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Just wondering whether to continue vacuum bridge clamping. When I vacuum clamp veneers in a large bag, my vacuum system quickly evacuates the air and shuts off. It will stayed sealed for at least a half hour or longer before the vacuum pump starts up again. When I vacuum bridges my pump never shuts off. It hovers around 22-23# of vacuum. The noise is annoying and I'm not sure the clamping results are any better than just using regular clamps. I've never really had any trouble with bridges coming off using my regular clamps, but the vacuum set-up is a little less dangerous. No clamps to fall over on the top or come loose. Just wondering if others are able to get the vacuum pressure high enough for their pump to cycle qnd shut down. I definitely have more line connections on my bridge clamping system, but have not been able to find obvious leaks. Thanks, Bob

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PostPosted: Tue Jun 08, 2021 5:24 am 
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That's about how my vacuum bridge clamp works too--it doesn't ever pull quite as much vacuum as my regular vacuum clamps or a bag, but pulls about the same as yours. My vacuum rig that I use for clampingdoesn't cycle, so I can't really comment on that aspect. I have a bigger, cycling vacuum system that I use for bagging that behaves like you describe.

I've still had so much better luck with a vacuum bridge clamp than I ever did using regular clamps or a Fox style clamp that I won't be going back.

Dave


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PostPosted: Tue Jun 08, 2021 6:19 am 
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I’m not geared for vacuum clamping, so I can’t recommend improvements there.

If you want to get back into regular clamping, the best bridge clamping for me has come from using three of the StewMac clamps that have the leveling feet. I use one over the middle of the bridge and one over each wing. Easy peasy.

I have experimented with a few different types of the Fox style clamping cauls and clamps, and they have disappointed me. The interaction between the different parts feels counterproductive; you tighten here, it loosens over there. Nothing works as well as three independent clamps, each doing their thing. That’s my experience, anyway.


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PostPosted: Tue Jun 08, 2021 6:36 am 
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Funny, I used a vacuum clamp for my bridges on new builds but quit when I started doing more repairs. I couldn’t get the vacuum clamp to work consistently when regluing bridges so just got used to using clamps. Now I use clamps on everything but I think vacuum clamping, especially for new instruments, is a good method.


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PostPosted: Tue Jun 08, 2021 8:24 am 
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I went back to clamps
I do more reglues so for me clamping works better

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PostPosted: Tue Jun 08, 2021 8:27 am 
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I do both depending on the instrument. The vacuum clamp really helps on ukuleles.

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PostPosted: Tue Jun 08, 2021 8:52 am 
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I have a continuous Gast pump and it runs the whole time but is pretty quiet. Pulls around 21 lbs the whole time. I also use for ukes, it's very convenient especially for smaller instruments where I forego a bridge plate. :)

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PostPosted: Tue Jun 08, 2021 12:13 pm 
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Thanks for the replies. I have no issues using regular clamps and a shop made clamping system, but I think the vacuum clamp does a somewhat better job at even pressure. Especially good for small instruments as John said. I just wish I could get it to cycle on and off for bridge clamping. I like the technology and glue cleanup is easier.-Bob

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PostPosted: Tue Jun 08, 2021 1:45 pm 
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I use a continuous run pump as well. Are you using the Joe Woodworker venturi setup that cycles on and off depending on pressure?


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PostPosted: Wed Jun 09, 2021 11:51 am 
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James- Yes, I built my pump from the Joe Woodworker site and it is the one that cycles off once up to pressure. I've used it for years for vacuum bagging and it works great.

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PostPosted: Wed Jun 09, 2021 2:19 pm 
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I also use a Gast pump and run it continuously. A bridge vacuum caul is a small volume and thus even small leaks will have a greater change on the vacuum inside the caul than they would in a larger bagging situation.
If one really wanted to make a super nice caul they could use some seals from these guys www.torrtech.com/Pages/Silicone-Seal.htm
I've used some of their T-7 seals at work, and they work great.

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These users thanked the author Jim Watts for the post: Pmaj7 (Thu Jun 24, 2021 12:55 am)
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PostPosted: Wed Jun 09, 2021 5:11 pm 
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I use the Joe Woodworker pump for bagging--works great, but it's a kind of big rig and made for big volume vacuum bagging, so for low volume clamping I have a small Gast continuous run pump. Also works great.

My Joe Woodworker pump was originally venturi, but I converted it to use with a pump since I no longer have my big air compressor.

Dave


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PostPosted: Thu Jun 10, 2021 8:27 pm 
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Jim Watts wrote:
If one really wanted to make a super nice caul they could use some seals from these guys http://www.torrtech.com/Pages/Silicone-Seal.htm
I've used some of their T-7 seals at work, and they work great.


The Torrtech site is very interesting. When I learned to make vacuum clamps in the early 1980's, we used 3/8" surgical tubing, and it worked great. Just rout a channel with a 3/8" half-round router bit, and glue the tubing into the slot with silicone sealant. A short, smaller sized piece of tubing goes inside the 3/8" tubing at the joint. Never had any problems.



These users thanked the author ThomLuth for the post: Pmaj7 (Thu Jun 24, 2021 12:56 am)
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PostPosted: Thu Jun 10, 2021 9:37 pm 
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ThomLuth wrote:
Jim Watts wrote:
If one really wanted to make a super nice caul they could use some seals from these guys http://www.torrtech.com/Pages/Silicone-Seal.htm
I've used some of their T-7 seals at work, and they work great.


The Torrtech site is very interesting. When I learned to make vacuum clamps in the early 1980's, we used 3/8" surgical tubing, and it worked great. Just rout a channel with a 3/8" half-round router bit, and glue the tubing into the slot with silicone sealant. A short, smaller sized piece of tubing goes inside the 3/8" tubing at the joint. Never had any problems.


That seems like a good idea.

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PostPosted: Fri Jun 11, 2021 7:31 am 
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I had a bridge that lifted at the ends of the wings immediately after unclamping with my vacuum clamp. Now I use the vacuum clamp, cam clamps on the wings and an ibex clamp in the middle simultaneously.

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