Mike Macartney

REPORTS ON A 1914 HUMBERETTE RESTORATION

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Mike,

 

I have done some steam bending using a similar set up using an old pressure cooker to generate the steam.   A bit of trial and error was needed to determine how much bend  was needed to allow for the spring back when released from the jig.  Also I had to work very fast to get the wood into the jig before it started to harden.   It worked very well after a little practice.

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David, 'spring back' is the problem that concerns me the most. I can find no formula for it anywhere on the web. I suppose it is just 'suck it and see'! I was going to try one bend at first and see how that goes. That may then let me know the amount of 'spring back', which I can then build into the jig. If all goes well with the test pieces I may well use the two pressure cookers I have and two steaming pipes and try and do both bends at once. Thanks for the tips. I have plenty of wood ready for 'turning into firewood' until I get the knack. The wood cost me nothing so a few mistakes will be a learning curve.

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Posted (edited)

I found a formula for spring back calculations, in metal of course. It can be adapted to wood if you can find out the Young's Modulus (and Poisson's ratio?) of the wood. I may be able to find it again tomorrow.

 

Found it almost immediately. http://www.custompartnet.com/calculator/bending-springback

 

You need Young's modulus and the yield stress, plus the K-factor (I can't remember what it is). You might be able to find those values for your particular timber.

Edited by Spinneyhill (see edit history)
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I now remember name 'Young's modulus' from my days at college doing OND & HND in engineering. It was a long time ago! Thanks for the link I will have a look and see if I can understand it.  

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Since my last post this morning I have been on the computer looking for information regarding 'spring back' in steam bent wood starting with Spinneyhill's link.

 

I found this interesting site

https://scholarscompass.vcu.edu/cgi/viewcontent.cgi?article=2051&context=etd

 

His conclusions were "To avoid the pitfalls of spring back found in steam bending elements the craftsman must learn to make designs which allow for and/or incorporate this factor. This factor cannot be accurately predicted with any success."

 

From all his experiments it looks as if I am on the right lines with my design and equipment, but 'just giving it a go' may be my best method!

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Mike, I'm scanning something for you... will see if I can attach it to a PM

 

jp

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The internet's been down today... I'll get back to this tonight.

 

j

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I have finally got up the courage to attack the repairs to the wings. If anybody has some tips to make this easier I would appreciate their help. It is many years since I have attempted making a round edge to a panel. And then I can only remember ever doing a 'wired' edge where the wire stays in the hollow section.

First of all I measured the section I am trying to reproduce on this rear wing edge.

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It's the area to the left of the photo. For the time being I am going to leave the brass edging to the back edge of the wing until after I seen if I can reproduce the small sections that need replacing. I may come back to it after I have repaired the other parts.

I worked out that the circumference of the 'bead' at the edge was about 1. Then cut myself a plate out of an old BMW 2002 door. 1-3/4" x 4" long. I find for panel beating metal to shape, that metal from an old car seems to form better, than new steel sheet. This plate I put in the blast cabinet to clean the paint off. Scribed a line at 1".

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A friend had lent me an edge joggler (or is it a Jenney?). I then put a crease in along my scribed line. So far so good!

Now how to roll the edge over into a tube? By dividing the circumference 1" (that roughly 25mm) by 7/22 (Pi upside down) it gave me a diameter of roughly 4mm. I was going to try using a twist drill as the mandrel for forming the edge, but found a suitable 4mm steel rod to use instead. The plate was then hammered in the vice to get nearer a 45 degree angle on the plate.

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I tried various method to try and bend the metal over the rod. If I need to make more of these sections to weld in I think I will make a jig. I wanted to see if I could make the part before I spent time on a jig.

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This method seemed easiest to start the bend.

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Plus this method to hold the rod in place.

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This is the same as the above photo but taken from the other side.

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It appeared to work and it needed some persuasion with a few taps to get it off the rod.

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The diameter seems a shade too large, but it is very difficult to tell as the beading is not absolutely round, it is more of a slight ellipse.

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I marked out the area I wanted to cut out with a felt pen.

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You can see in this photo that the edge is slightly curved. Anybody got any thoughts on how I can achieve a slight curve? I tried using my leather sandbag and a hammer on the flat surface but the 4mm diameter tube part is trying to hold the plate in a straight line. Perhaps a bit of heat may help to get the correct curve?

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The underside of the plate looks pretty good. I am quite pleased apart from feeling knackered after using my brain cells and hammering away for 3 hours.

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I did think maybe I would be better off shaping the plate in the wheeling machine before I tried to make the round bead. But then I realised that by using a rod to make the bend it would straighten the panel back. I think some heat maybe the answer? I bought this 'wheel' about 4-years ago when I was persuaded to sell my proper big Edwards English Wheel - I now wish I hadn't sold it. As yet I have never used this small wheel - it looks as I will have to modify it so that it will fit in the vice. At present the 'T' bar that put's the pressure on won't turn because the bench is in the way. Maybe I'll do that tomorrow when I have 'recharged my batteries'!

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I think I'd try steaming some short pieces first - both to practice and to measure the spring back. Then go to the full-size pieces.

 

 

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How about sliding the mandrel back in and pressing it against something with the right curve. The radius should be shallow enough so that the mandrel can be pushed or tapped out.

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Can you insert a solid wire into the rolled area for support while bending into the compound curve?

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5 hours ago, keiser31 said:

Can you insert a solid wire into the rolled area for support while bending into the compound curve?

 

Yeah, but that would be cheating. ;)

 

You might make a significantly longer section (maybe 2x or 3x) and try bending that over a similar radius (with the solid wire in the rolled area as keiser suggested).  The bigger section will give you some leverage and over the length of the bend (which, of course, not be consistent) you'll probably find a section that fits nicely.

 

Edited by Luv2Wrench (see edit history)

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Mike,  

How are you planning to weld in the repair piece?   If you oxy weld with steel rods you will need to either cut out all brazing or braze the new piece.    Steel welding alongside brazing produces a brittle alloy that will crack.

 

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And have you considered leaving the wire in there after curving the piece? The only rolled edge mud-guards that I have played with had the wire in the roll for strength.

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I agree with Bush Mechanic.  It is called a Wired Edge.

     

If you cut the damaged part of the fender away carefully you may find the original rod or part thereof still in place.  If so, you can semi form the patch,  weld it in place and

heat / beat the new plece around the existing rod.

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14 hours ago, JV Puleo said:

I think I'd try steaming some short pieces first - both to practice and to measure the spring back. Then go to the full-size pieces.

 

 

"Great minds think alike" - I have four large planks of the sweet chestnut and there is the remaining three quarters of the fallen tree to use, if we run out of planks of wood. I was going to have a few practise runs with just one bend first. After, reading the 58 page University thesis, that I mentioned in one of my posts. The problem they seemed to have was the strength of the metal straps. Experimentation as you suggest is the best option. I will mark the jig up with different angles and make notes on the spring back The only time constraint is April when the car is due at the coach trimmers. He wants the car for three months, but he could do the inside work first before moving onto the hood. Therefore I have plenty of time to make lots of kindling for our wood fire out of the mistakes!385.thumb.jpg.47cf0bddfd89cce8d8a6d8a3bb19c144.jpg

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JV Puleo - How about sliding the mandrel back in and pressing it against something with the right curve. The radius should be shallow enough so that the mandrel can be pushed or tapped out.

Joe, the problem there is that with the 8mm diameter bar. After I had beaten the metal around the bar, the bar was a tight fit in the 'tube' part. If I did manage to bend it with the bar in place I would not be able to get the bar out afterwards. I suppose that I could cut the ends off the bar and leave the bar in place after bending?

 

Keiser31 - Can you insert a solid wire into the rolled area for support while bending into the compound curve?

Thinking about your post is making me think that may be the solution. (see above reply to Joe).

 

Luv2Wrench - You might make a significantly longer section (maybe 2x or 3x) and try bending that over a similar radius (with the solid wire in the rolled area as keiser suggested).  The bigger section will give you some leverage and over the length of the bend (which, of course, not be consistent) you'll probably find a section that fits nicely.

I like the thinking behind this, apart from the time it took me to make a short piece!

 

DavidMc - How are you planning to weld in the repair piece?   If you oxy weld with steel rods you will need to either cut out all brazing or braze the new piece.    Steel welding alongside brazing produces a brittle alloy that will crack.

I realise this. That is why I was going to cut out a longer section than needed to get rid of the existing brazing. If I do end up keeping the brass repair to the bottom of the wing (I realise know I should have been calling it a fender) I could silver solder the end of the brass to the new metal plate after the rest of the welding was done.

 

Bush Mechanic - And have you considered leaving the wire in there after curving the piece? The only rolled edge mud-guards that I have played with had the wire in the roll for strength.

I too have only ever come across rolled edges that have had a wire inside the bead. This is the oldest car I have ever had to repair the wings on though. With 8mm rod inside the beading it would certainly be strong.

 

DavidAU - If you cut the damaged part of the fender away carefully you may find the original rod or part thereof still in place.  If so, you can semi form the patch,  weld it in place and

heat / beat the new plece around the existing rod.

I will be cutting the section out this morning. I will be surprised if there is a rod or wire inside as where the metal has rusted away there does not seem to be a wire behind it.

 

My thoughts overnight and after reading all your posts this morning.

 

Last night I thought of maybe using Kunifer piping inside the bead as this would bend easily. Then I thought that this may react with the steel. I then looked up steel brake piping on the internet and then small diameter tube. I can get Kunifer at 8mm diameter but the 1mm steel pipe is only available in 5mm OD, 6mm OD and 10mm OD. Your thoughts on using tube as the centre of the beading would be appreciated.

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12 hours ago, Mike Macartney said:

 

My thoughts overnight and after reading all your posts this morning.

 

Last night I thought of maybe using Kunifer piping inside the bead as this would bend easily. Then I thought that this may react with the steel. I then looked up steel brake piping on the internet and then small diameter tube. I can get Kunifer at 8mm diameter but the 1mm steel pipe is only available in 5mm OD, 6mm OD and 10mm OD. Your thoughts on using tube as the centre of the beading would be appreciated.

 

Mike, I see now that the rolled edge is substantially thicker than it appears in the photos.

 

I have seen steel brake pipe used as reinforcing at stress points, tucked up behind a flange and welded into place.  It has worked well on the bonnet of my Healey for 20 years. There is a stress point where the prop supports the bonnet weight, and the flange had cracked through. Actually I had forgotten it was in there, but I think it is 5/16". The gentleman who suggested using it is a talented body man, and I have no complaints with his advice.

Edited by Bush Mechanic
Clarification. (see edit history)
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Bush Mechanic - Thanks for the post regarding the steel brake pipe reinforcing the bonnet on your Healey.

Yesterday I first of all got stuck into sorting out the small wheeling machine so that it would fit in the vice and be useable. As the bench is not that strong I may have to modify it again to fit on the table of my milling machine. The mill table is nice and sturdy and makes a solid base for lots of bits of equipment.

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I cut a couple of lengths of 2" x 1" box and marked the position where I wanted to weld them to the frame.

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After grinding back the edge where they were to be welded to the frame I tacked them together with the MIG welder.

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Then turned them round in the vice to put some more tacks in to hold them together.

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Turned them over and welded the other side.

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I had not ground enough of the blue paint off the frame so it caused problems with both the welding and my lungs (more about that later).

You can see the welding problem in the photo, it had caused the weld to build up on the torch shroud.

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With the bottom extension parts added it now fitted in the vice and the T-bar pressure adjustment would rotate OK.

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The upright that holds the replaceable bottom wheels leaves a lot to be desired! It's a bit sloppy in the box section. I will give it a go and see if it works before making any modifications to it.

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After your suggestions about there being a wire in the edge beading I cut a section out the wing and edge to check.

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As you can see by the scriber disappearing up the hole.

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I was pretty sure the round edge I had created yesterday was too larger a diameter. This photo proves it. At least now I could establish the inside diameter with a drill bit and then try and find some suitable steel tubing to use as a mandrel that could stay in the round hollow section.

I thought I may find a bit of old steel brake piping in my daughters second hand BMW parts shed full of parts for 02's and CS models.

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Finding nothing but copper and Kunifer replacement brake pipes I wandered back to my shed, when I spied a pile of old parts waiting to be sorted. There was a length of steel brake pipe attached to a rear crossmember and swinging arm.

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A quick grind at each end and it was off.

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A quick check by 'poking it up' the open end up the hollow section proved that it was the right size. Now to clean the brake pipe up and see if I can use it to make another section of wing (fender) to weld in.

 

 

 

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As this old length of brake pipe had brake fluid in it. I cleaned it in cleaning thinners.

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With the 'hooked' end I scooped up some thinners and then turned the pipe up the other way to drain out the thinners and hopefully the brake fluid.

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It seemed to work and after a few rotations the brake fluid was out of the pipe.  If I had not cleaned the inside of the pipe the brake fluid may have leaked out after the wing had been painted and damaged the paintwork.

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A grit blast in the cabinet and the pipe cleaned up OK.

Now to find out the outside diameter of the pipe.

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And then the thickness of the metal.

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I now had all the information I required to do the calculations for the width of metal I needed for the 'turn over' for the hollow edge.

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It seems that 17mm should be enough.

Before starting on making a new section for the wing (fender) I decided to check the rest of the wing to see if there were other areas that needed repairs.

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It looked as if a plate had been soldered on to the underside of the wing in the area of the bolt fixings. After a trial 'grind' it appeared it was solder.

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The butane torch melted the solder.

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And I was able to brush the worst of it off with a wire brush.

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I then used the mule skinner in the drill to get off the rest of the solder.

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The solder 'debris' was' Hoovered up'.

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I also cleaned up other areas where there was 'lumpy' solder.

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This previous welding leaves a lot to be desired! In the trade we used to call it 'Pigeon Shit'! Do I try and clean up the welding or cut the section out and put in new metal?

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I decided to have a go at cleaning up the welds and see what it looked like. I used the angle grinder first with a cutting disc fitted.

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The underside was a lot easier to clean up than the other side. Most of the rest of the morning was spent trying to tidy up this area. I think it would have been more sensible to make a new section. I'll think about it overnight.

 

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This was the mess I was left with. Plus all the 'stuff' on the bench. Looking at this photo I must make a note to cover MGB with a proper cover before I do some more grinding.

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This is a photo of the bottom end of where I had out the bad section of the fender. I am thinking that at this end of the patch I will have to have a go at silver soldering the brass to the steel.

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I was cleaning up this area with the Mule Skinner and this happened . . . .

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. . .  the wire brush slipped off the panel and caught my overalls! Lucky it didn't get me in the crutch area!

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This end appeared to have broken away at the end. It looks as if this 'valence section' is soldered on to the fender.

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I removed some of the solder with the blow torch and cleaned up the area.

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The Dremel cutting discs were starting to get a bit out of balance and wobbling when spinning quickly. I replaced the SpeedClic arbour with a new one. They wear badly when you try and use the last of the cutting disc.

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It worked a lot better with the new arbour.

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I attached the rear fender stay to check it fitted the hole OK.

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Now to weld up the ends of the valence to the main part of the rear fender.

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I was a bit worried that this weld may not take because of the solder. I just hoped I had got rid of most of the solder in that area.

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One end worked OK, but this end looked a bit messy. The 'dribble' line you can see is from when I tried the brake pipe in the hole. It will be interesting to see if it affects the 2-pack etch primer. I'll clean that area with panel wipe when I get into the garage tomorrow morning.

Next, I'll have go at making a new patch for the fender using the steel brake pipe as the centre of the rolled edge.

 

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Great pictures and narration!  From where I'm sitting (and I'd probably have a different opinion if I were there holding the wing) is that I'd do the patch in two pieces.  I'd have a tube for the rounded section and flat sheet metal for the rest and assemble the two "in place" on the wing.  I'd have a smaller OD tube/wire go into the the existing rounded section and also into the new 'tube' to help indicate the tube and hold it.  Then weld in the sheet metal and a little lead filler and/or body filler to match the profile on the rest of the wing. 

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If by chance the original construction of the mud-guard utilised solder, is it possible that the patch at the bolt holes was an original reinforcing piece? Of course the solder may have been used in a later repair, but the holes do not appear to be torn.

 

And as Luv2 suggested, an over-length piece of brake pipe slipped into one side of the cut rolled edge, and then teased back to also pick up and enter the other side roll, would go a long way toward strengthening your repair. It would give you a solid profile to work the sheet steel to.

 

The Alaskan chainsaw mill used on the log brought back a lot of memories. I milled a quantity of beams and posts with one when I was young and silly, and it was definitely hard work, in Australian hardwood.

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21 hours ago, Luv2Wrench said:

Great pictures and narration!  From where I'm sitting (and I'd probably have a different opinion if I were there holding the wing) is that I'd do the patch in two pieces.  I'd have a tube for the rounded section and flat sheet metal for the rest and assemble the two "in place" on the wing.  I'd have a smaller OD tube/wire go into the the existing rounded section and also into the new 'tube' to help indicate the tube and hold it.  Then weld in the sheet metal and a little lead filler and/or body filler to match the profile on the rest of the wing. 

 

I agree. That may have been the simplest solution. I wanted to test myself to see if I could make the section to fit in. On the section you are writing about the tube fitted in one side, but on the lower side where the brass bead is the section is not hollow. Otherwise I would have tried to push the 'steel brake pipe' mandrel into both hollow sections. You will see that it all worked out OK in the end, in my next posts.

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