RE: Reversing hide glue on a molding plane

David Conley

Well-known member

I just got a match set of snipe molding planes that I plan to use.  However, the hide glue between the boxing and the plane body is in various states of failure.  On the first plane, I was able wiggling the front and back pieces of boxing out of the plane.  On the second plane, I was only able to pull out the front piece of boxing.  The hide glue is probably 70 % failed on the remaining piece of boxing (see photograph).   The problem is that it caused a heavy 1/16 inch separation between the boxing and the plane right on the bed of the blade.  This piece of boxing is also flexing up and down as you place pressure on the plane.  So, I have to repair it.

I do not expect it would take much to reverse the hide glue and free the boxing.   My question to the group is: how do I reverse the glue and NOT warp the plane in the process?  

In 2007, there was a post Re: Reversing Hide Glue in the Conservation and Furniture Repair section of this forum, I saw several methods mentioned.

1) If you did not clamp the joint, i.e just "rubbed on" the knee block, the glue joint will be weaker than the surrounding wood. You can usually tap it off with a hammer or lever it off with a clamp.

2) Apply heat with heat lamp or heat gun. This will often soften the glue enough to remove the knee block. Avoid getting nearby joints hot.  

3) Steam the joint. This won't hurt the wood but if the steam gets to nearby joints on the leg they too may loosen.  

4) Drill a large hole through the knee block stopping just past the joint line. Fill the hole with alcohol/acetone or even water. This will usually loosen the joint.  

5) If you heat up the joint just a bit you may use a syringe filled with alcohol and inject it into the joint. I have had good success with this process. In addition, you will not loosen other joints that are nearby.?

I tried the #1 method on this plane and knocked the front boxing loose.  I could not free the back boxing.  

I am tempted to try method #2 by placing the plane on top of my glue pot for a couple of minutes.   If that does not work, I am planning to try method #5 by placing some alcohol in the open joints.  

Am I on the right track?

Thanks in advance,


  • Snipe plane boxing separation.JPG
    Snipe plane boxing separation.JPG
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David, Methanol (wood alcohol, what you can get at your local hardware store) will release hide glue. It is poisonous to consume. What works best is Moonshine, accessibility is another question but we won't go there. I used to live in Franklin County, Virginia known for it's hand made alcohol. It will release hide glue (among other inhibitions) quickly. Watch your eyesite too.
Denatured alcohol from the hardware store is ethanol (moonshine), denatured with methanol (wood alcohol). This will work fine to loosen up the hide glue. Take a flat plan and stand the plane up in a 1/2' of denatured alcohol. Manipulate the boxing so that the alcohol gets in. Heat from a heat gun or heat lamp will work too.

Howard Steier
Howard, Thank you for you clarification. I have other comments about releasing hide glue but I would not want to misrepresent more than I already have. It doesn't take much alcohol, it will leach up a hide glue joint. Crystallizing the hide glue. I would think that heat might introduce new problems. I might refrain from heat.
Jeff and Howard,

I am not sure I want to end this discussion.  I find it interesting that both of you lean toward the alcohol as your preferred method.   My first question: is the alcohol you are talking about is the Denatured Alcohol (shellac thinner & alcohol stove fuel)? I get from Lowes?  

My next question: is how fast does the alcohol penetrate the joint?  For example if it is a tight ? inch glue joint for a through dovetails, how long will it take the alcohol to loosen the joint?  And I know that this is highly dependent upon the glue, the glue joint, etc, etc, but how long do you flood the joint before you expect the glue to soften up?  15 seconds?  10 minutes?    

As for my molding plane, I heated it up by laying in on top of my hide glue pot.  I then picked it up in my hands and flexed the joint until it broke loose.  There really was not much holding it together.

It takes a while; not just a few minutes. Thats why I suggested immersing it in alcohol and manipulate the boxing from time to time so that the alcohol can seep into the joint.
Yes, this is the denatured alcohol that you buy at Lowes.

Howard Steier


When I glue the boxing back in, I’m going to make up a test piece and try this out. 

My suggestion for refraining from heat comes from what that might do to the movement of the released piece especially on a hand plane to keep it true. Maybe I am being overly concerned. Alcohol doesn't loosen a joint it crystallises the hyde glue enabling you to separate the glued surfaces from what basics that I have been told.

I've had this same problem on a few molding planes and have had to reattach loose or missing boxing too. Always on English planes, interestingly. (Difference in humidity between Jolly Ole England and my shop in VA I suspect).

Fortunately, the boxing has always just fallen out or was *priable*. I've never had to resort to moonshine or moonshine lite, so I'm thankful for this discussion in case I need a more scientific solution to this problem on future acquisitions.

Nothing to offer other than a question. Are you going to reattach using hide glue? I would recommend it as you never know but those snipes may not be done acclimating and you might have to (through no fault of your own) work on the boxing yet again.


Rick Yochim 

Funny you mentioned English planes.  I just got these off of Ebay from England.  So, the change in humidity did not have a chance to kick in.  The glue joint was shot when I got them.  Maybe it was the hide glue itself, 100 years of high humidity, or some other degradation?  

I had not thought about allowing these planes to acclimatize from England to my basement.  While writing this, I checked the moisture of the planes and it was a consistence 15%.  My other planes read between 11 to 12%.  Heck, last Saturday I brought in an ash board into the basement that had been sitting outside for a couple of years and it read 16%.  Now I am thinking I should wait about a month before I do anything to allow the moisture to get down to approximately 11 to 12  percent.  

OK, I just freaked out and placed some fairly heavy steel bar stock into the snipe's dado and clamped the planes against each other  (an ounce of prevention is worth a pound of cure).  These planes were flat and straight before I started, and I do not want to take a chance on messing them up.  

David- The boxing comes out eventually because the grain in the boxwood runs perpendicular to the grain in your pane. I don't know if all boxing does this, but I think the ones I've fixed in the past have-Al

It's somewhat nasty stuff, requiring very good ventilation: Benzene aka Naptha. The glue will soften, even crystallize (at least it looks like that to my non-chemistry eyes) and allow removal of the boxing, chair part, tenon or whatever. It works on hide glue. Never tried it on yellow PVA glue.

This stuff has a low flash point, so it should never be used near open flames. A fume mask or chemical mask is a good idea if you have one, else good ventilation and a fan to exhaust the stuff.

I use a small ancient brass oil can, little tiny thing. Just fill it with a little fluid, dribble in the joint, wait a bit, dribble some more, wait a bit and see if things loosen up.


I have been thinking about how the alcohol crystallizes the hide glue.  However, I would really rather have a medical doctor pipe in on this and share their knowledge.  From my own personal experiences with shellac and alcohol, the alcohol removes the oils from the skin.  Napthe, acetone, etc, are just more aggressive.  My theory is that these fluids are removing the oils from the hide glue.  This in turn, breaks down the hide glue bond.  The wood also helps to transport the fluid right to the glue joint.  It all kind of works together to breakdown the joints.

Update on the planes:  The moisture meter ranges between 13 (thin sections and ends) and 14 percent (thickest section in the center of the plane).  The lowest reading was 12.  I am guessing it will take another month or two before the moisture drops to a stable reading. 


A good idea. I'll pass this along to some people who may know more of what really happens and see... what happens.

Update:  after 3.5 years, I finally (thanks to the Federal furlough) got around to putting the boxing back in the planes.  The moisture content is still around 13 percent.  That really surprised me.  I thought the moisture would have dropped to 7 or 8 percent.  It must have been the old coats of linseed oil.  

I had to reduce the thickness of the boxing a little to get it to fit back into the dado.  Once I got a snug fit, I dry fitted the boxing and marked the location of the end of the flat ends of the boxing on the plane body with a marking knife.

I used a thinned hot hide glue and painted the boxing and a then a quick swipe down the outer edges of the dado.  I did not put hide glue in the bottom of the dado because I did not want it to swell the plane body.  I figured if it did, I would not get the boxing to full depth.  I was really glad I scribed a knife line on the plane because it gave a good reference point in adjusting the boxing to.

I quickly sharpen the blades, and they work pretty well, but I need to spend some time on adjusting the profile to get them fully functional.


You must be one organized and patient dude, dude. I can't remember, let alone find, all the projects I left unfinished from three years ago.

Howard Steier