Soapstone bridge removal "iron"

Construction and repair of Classical Guitar and related instruments
SteveL123
Posts: 548
Joined: Thu Feb 09, 2017 5:05 pm

Soapstone bridge removal "iron"

Post by SteveL123 » Thu Jan 04, 2018 4:58 am

As a first round in my experiment, I made this bridge removal "iron" out of soapstone, heated with an electrical rod heater controlled by a SSR/ PID controller/ thermo-couple. It got my test mule bridge off that was glued with Titebond Original once I got the temp to a good level.

I will build another one from lessons learned from this one:

1. Trying to heat a wing and the tie block part of the bridge at the same time is cumbersome and unnecessary
2. Need more weight - use a bigger piece of soapstone
3. Move the thermo-couple from the top to the bottom for better temp control.

The bridge came off clean without splintering the pine.

Some pics and a video. The video was trimmed from a long video and my phone ran out of battery just before the bridge came off. In the last part of the vid. I was rocking the soapstone on the curved wing to make better contact. In the next one I make, one of the surface will have a curve matching the wing for best contact/ heat transfer


Youtube

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Last edited by SteveL123 on Thu Jan 11, 2018 3:31 am, edited 3 times in total.

SteveL123
Posts: 548
Joined: Thu Feb 09, 2017 5:05 pm

Re: Soapstone bridge "iron"

Post by SteveL123 » Sat Jan 06, 2018 7:55 pm

Image

Anyone used one of these bridge heater/ fingerboard iron made from a block of aluminum? How long did it take you to remove a bridge? Is there a time difference between a bridge fastened with hot hide glue vs Titebond?

I am finishing up my second iteration soapstone bridge iron and would like some data for comparison.

SteveL123
Posts: 548
Joined: Thu Feb 09, 2017 5:05 pm

Re: Soapstone bridge "iron"

Post by SteveL123 » Mon Jan 08, 2018 3:24 am

I used a bigger piece of soapstone with a shorter heating element. I also coated the chalky soapstone surface with high temp RTV that is good to 500F. The RTV makes it less slippery and also less abrasive against the bridge. I think it will also make better thermal contact. The hole drilled for the heating element is not a snug fit so I filled the nooks with soapstone dust from drilling before RTV'ing it in place.
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SteveL123
Posts: 548
Joined: Thu Feb 09, 2017 5:05 pm

Re: Soapstone bridge "iron"

Post by SteveL123 » Tue Jan 09, 2018 3:41 pm

I've been having problems uploading videos to youtube that are longer than 15 min even though I "verified" my account. Maybe there's a wait period before it takes effect but it works now.

Here's a full length (quite boring) video using my Soapstone bridge "iron" to remove a test mule bridge glued to an approx 1/4" thick pine board with Titebond original. As you can see, I started with a setting of 250F which was not hot enough and kept upping the temps.
I had to finally set it above 400F for it to be effective. Maybe a block of aluminum would require a lower setting being a better conductor. I am not going to make an aluminum one and will keep on testing this one.


Youtube

SteveL123
Posts: 548
Joined: Thu Feb 09, 2017 5:05 pm

Re: Soapstone bridge "iron"

Post by SteveL123 » Tue Jan 09, 2018 3:50 pm

This is another video of the test mule bridge glued with liquid hide glue (from a bottle). This hide glue seems to be easier to get off than the Titebond. I'll have to do a few more tests to confirm. I started with above 400F setting and didn't turn the camera on till after approx 5 min of preheating the bridge. I am going to add a handle to this iron for easier handling.


Youtube

vesa
Posts: 476
Joined: Tue Mar 01, 2016 12:52 pm
Location: Sulva, Finland

Re: Soapstone bridge "iron"

Post by vesa » Tue Jan 09, 2018 5:08 pm

Interesting to follow Steve, thanks for sharing.
400+ is quite hot, does the heating element have any effect on RW,
does it get darker because of the heat?
Vesa Kuokkanen

Antonio Marin nr. 813 1995 (Bouchet)
Vesa Kuokkanen 2016

SteveL123
Posts: 548
Joined: Thu Feb 09, 2017 5:05 pm

Re: Soapstone bridge "iron"

Post by SteveL123 » Tue Jan 09, 2018 6:06 pm

vesa wrote:
Tue Jan 09, 2018 5:08 pm
Interesting to follow Steve, thanks for sharing.
400+ is quite hot, does the heating element have any effect on RW,
does it get darker because of the heat?
Vesa, the heating element is in the center of the block of soapstone, not direct contact with the wood, so is less likely to scorch the wood. I do not see any burn marks on the rosewood, maybe that is because the rosewood is dark to start with. I will test it against a piece of cedar and see if it darkens it.

SteveL123
Posts: 548
Joined: Thu Feb 09, 2017 5:05 pm

Re: Soapstone bridge "iron"

Post by SteveL123 » Wed Jan 10, 2018 1:30 am

Did a test with a piece of cedar shim stock from Home Depot. With the PID temp controller set to 410 F and Soapstone sitting on top of it for about 30 minutes, it darkened the cedar a little bit (top of pic). I doubt you'll see a color change on rosewood. I lowered the temp to 350 F and placed it right below the darkened spot and it is darkened a bit less.

When bending sides, what temperature is the heater set to?
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SteveL123
Posts: 548
Joined: Thu Feb 09, 2017 5:05 pm

Re: Soapstone bridge "iron"

Post by SteveL123 » Thu Jan 11, 2018 2:54 am

In the last 2 bridge removal tests, the spatula felt very sticky and I had to push hard to work it. I think that is due to the cooling effect of the spatula making the softened glue harder. So I thought, why not make an electrically heated spatula?

With some Nichrome wire, mica insulation tape and self fusing silicone tape I made one which runs on 12 volts. I estimate it is putting out around 8 watts. It does help make cutting through the thick glue much easier, I used it in my next test (uploading now, post video link later) which was glued with hot hide glue.
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