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martin35
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08-17-2019, 06:03 PM

Quote:
Originally Posted by kid View Post
Maybe just a simple sheet of aluminium with the same finish as the corners could be nice ..


Envoyé de mon iPhone en utilisant AzBilliards Forums
Hello Kid

Nice to hear from you.

I like the idea but I wonder if the Aluminum may damage the bridge stick, but on the other hand it's only a bridge and not a cue.

I think it's good idea but I had my share of aluminum polishing for a while.

Thanks

Martin
  
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Boxcar
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08-17-2019, 06:03 PM

Martin,

You will enjoy the website known as:

Constantine's.com

They have a vast inventory of veneers. You may be delighted to find the "Flexible" veneers sections.

Best regards,

BOXCAR
  
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Ssonerai
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08-17-2019, 07:35 PM

Martin -

Not being intentionally generous
This is interesting enough that it informs other work i do.
And it is relatively fast to prototype. Cnc router would be really fast. I'm oldschool and use pinrouters and such. So once a master is made, it is quick to duplicate, make the mating part, etc, etc.

The 90° bend seems borderline to me, so i wanted to be sure i was not mis-stating anything. I'll show the work, then discuss some factors to improve the process. This computer times out too fast and the post gets lost.

First photo is 2 layers 1/16" thick birdseye maple, it is black because it was scrap form a project that used it ebonized. I tried this several times with no success. Only 1/16" i had on hand other than mahogany, which also broke immediately.

Second photo is 3 layers Birdseye maple, .048" thick - success!

3.) is 6 layers .048" BE & plain mixed. This is thicker than the press design, and even at that small difference, begins to show errors - there is a gap at the peak of the 90° bend if you look closely.

4.) is the press design thickness at .260" and includes 5 layers .048" + one layer compressible naugahyde at .039" for compliant pressure. Adding a compressible layer on the follower side helps immensely to force conformance with the control surface.
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Ssonerai
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08-17-2019, 07:51 PM

The only reason the press design thickness was .260 in the above example, is that the follower pattern was directly routed from the master. The pin was a bit larger than .250, a .250 router bit was used, and light sanding cleaned it up. So in this case, convenient tooling defined the follower space.

I wondered what kind of force it would take to close up the press, after the strips had been clamped already for previous pics. This is really crude, but informative. (Part of my weight is resting on elbows to steady the camera; I do weigh a little more than shown) Not clearly visible, but 150 lbs is not really enough to fully force compliance at the 90° peak; however it gets most of it.,

On the real form, the angles need to be slightly exaggerated - like maybe 89° instead of 90°. 136° instead of 135°. It all depends on thickness and number of lamina, and the type glue.

It is better if the control form is really stiff and rigid. However, the follower should be a lot more flexible than shown. it should be able to conform to the control, so long as it adequately presses the veneers in hard on the tricky areas.

The strips are 1-1/2" wide. So if it takes 150lbs to "mostly" attain the form, that is 100 lbs/inch width. the strips are 11" long, but most of the pressure is concentrated on about a 5 or 6" section. So 16 - 20 lbs/in^2. This is where vacuum gets iffy. It might pull it all down, but it is borderline at the veneer thickness and total part thickness. Not all your layers would be long grain, so that is in your favor, wood bends easier "sideways". The good thing about vacuum is that at this thickness, i doubt there would be voids. It just might not pull down exactly to form. I would definitely do a dry run and include every step.

good luck!
smt
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Boxcar
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08-17-2019, 08:10 PM

I apologize for this interruption. You certainly already know this, but the grain of the bridge rack runs at right angles to the grain of the veneers in your demonstration. You have achieved remarkable results with your multi layered veneer sample.

Best regards,

BOXCAR
  
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Ssonerai
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08-17-2019, 09:36 PM

Boxcar - Sounds like you've bent and veneered a few things!
Unless i interpreted the pictures wrong, the grain goes both ways, like common plywood. That would also be the only really practical way to make the full length part.

As you are allowing, the crossways grain (to the shape) is the most difficult, so i just did the pressures and such "worst case". Always better to find the real thing goes easier. It would be worth bending a few parallel grain samples over the peak by hand - won't take much pressure at all, but worth finding out how likely it is to break.

Still, big changes occur with small differences in veneer thickness, total thickness, and small details like just making the 90° radius larger.
So from here the jury is out until some actual measurements or comparison with a real part happen.

PS: It looks like Blat Billiards gets their veneer from certainlywood in East Aurora, NY. (Buffalo).

smt
  
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Boxcar
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08-18-2019, 08:42 AM

SMT,

You do amazing work and it is clear to see that you always evaluate the variables.

Your table aprons are fantastic. It appears that the grain of each ply runs long. Is that what I am seeing?

I think the original bridge racks were three-ply. The outer plys certainly ran long. Was the inner ply laid at right angles?

It's been years and I have forgotten a lot. Did Plycraft and Knoll/Eames chairs lay up on the cross or long?

This is an interesting study. Thank you.

BOXCAR
  
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Ssonerai
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08-18-2019, 08:45 AM

Worth clarifying a couple points.
The questions a bending project poses are 1.) will vacuum bend the parts (will it develop enough pressure, since the limit is 14PSI. 2.) what thickness veneer will bend over/into the worst section radius reliably without breaking.

Vacuum (or generally, also pressure bladder) will bend thicker veneers without breaking them, than a 2-part top/bottom hard press, because the vacuum pressure starts on the peaks, and "smooths" the material out and down both sides while compressing and supporting it at, over and around the peak.

Veneers which break when hand bent for trial over the difficult sections, may vac or pressure bag press successfully, yet pop grain here and there on thick faces when removed from the press. However, these considerations show why thicker core veneers can be used successfully with slightly thinner face veneers.

smt
  
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Ssonerai
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08-18-2019, 09:20 AM

Boxcar - you and i were typing at the same time.

Thank you for the very kind words.

Quote:
It appears that the grain of each ply runs long. Is that what I am seeing?
No, these have alternating layers just like plywood.

The "old dead guys" often veneered burl right over solid wood for curvy stuff, because burl will sort of shrink/expand both ways. On better work where a cross band could be applied, they did use that.

I did not want the risk of uncontrolled shrinkage or expansion for several reasons. I did not want the drawer space to vary, did not want the risk of veneer popping, and the interior dividers are plywood again for stability, so not making the outer skirts the same would risk the carcass fighting itself over time and seasons change.

i neglected to take pics of the actual stacks laid up for bending; but here are some from veneering them that show cross plies. The inner cores are the same, alternating layers.

Ray and Charles Eames chairs, and all the clones ever after are full plywood alternating layers of cross and long grain.

The replica curved church pews i built ca 1991 for a congregation that had expanded their building always puzzled me as to how they did things in the 19-teens. With only hot hide glue to work with!. The backs of the original pews had a very thin center cross band, and thick outer plies. I have always wondered how they bent the 3-d shape back then. End to end long radius is easy, of course. But the top to bottom S-curve "Back shape" added onto that must have taken an interesting press. I do know they used concret forms for some work at least by the early 1920's but have no idea if that was applicable for the church pews. For modern work it was easy with a single side form, WEST, and vacuum.
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Ssonerai
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08-18-2019, 09:28 AM

Limit 5 photos per post.

This is the underside of the bottom panel. QS sycamore.
There's a story behind sheltering under (in) hollow sycamores in the clients family history.

smt
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08-18-2019, 12:27 PM

Great historical reference. Thank you.

I was an AWI affiliate back in the 70s, 80s, and 90s. Seeing your shop makes me homesick. I still have your scraper(the one on the right)in my tool box.

We did an awful lot of circle head sash and door frames for one of our well known period restoration contractors. We bent a lot of NE WP and some Hond Mah and we had a steam chamber that was very helpful. I'd have to say that 100% of our bends ran the grain long. We mixed waterproof brown powder so it was easy to set the viscosity and cure time.

A major ship builder near me used miles and miles of Hoover laminated wood fire retardant scaffolding. The scaffolding was load bearing. My memory is that all of the plys ran long. There was no loss of lateral or longitudinal integrity. My point, of course, is that laminated products which lay up parallel grain components are suitably strong. It would seem that post-formed components layed up with their grain running parallel would be more than suitable for these bridge racks. Even if Martin went from a 3 ply to a 5 ply build, things should work well. We always felt that glue was stronger than wood. Please share your thoughts.

Best regards,

BOXCAR
  
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Ssonerai
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08-18-2019, 08:24 PM

Boxcar-

Running all the plies longways is both stronger, and nicely more convenient for many items. Certainly most of my architectural millwork was run long grain. I had a small milllwork and installation business/crew, and we worked in DC & Manhattan. Lot's of arch windows, replica or new work, lots of doors of all shapes. Some curved both ways.

Seats and "thin" stuff or other 3D bends, it is usually best to have a cross ply or more for shape stability & to prevent cracking.

It is good you continue to "press" on the immediate subject, the triangle rack. I was taking it as 5 ply. Often on constructions like that, the face is thin and with the edge beveled or rounded, it is not really perceptible on a stained part. But studying the eBay item, i think you might be right that it is 3 ply.

Doing it that way should certainly be easier. My only minor concern would be that the part should be over-bent, it will have more springback with only a few thicker plies. However, Martin (IIUC) was initially speculating that it could be 1/2" or 3/8" thick. Studying the eBay item, it seems about 1/4" thick. 3/32"-1/16"-3/32"? The eBay item also seems to have a continuous round section where the above drawing shows the 1" radius 90° bend with a short straight. Those differences for all parameters start to suggest a very easy vacuum bend.

Further speculating or testing without some assured numbers seems pointless.

smt
  
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08-18-2019, 10:15 PM

SMT,

Excellent post!

So now, the mission may well be one of creating an authentic period replacement part. Brunswick was in a roaring, post war footing in the mid to late 40s. They were trying to make up for war time losses, which is to say they weren't worried about competing with Steinway. These racks were entirely utilitarian, and were surely designed to be CHEAP, cheap to build and built of cheap materials. If I had been the design engineer on that part, I would have made it 3/8" thick and out of three 1/8" plys fresh from the plywood mills. The core and the bottom would have been trash and off-fall and the face would have been the prettiest piece of trash left in the bins. I'd have slapped those muthas together in a press that anticipated an acceptable amount of recoil, made 500 at a pop on the clamp carrier, pulled them, shaped them on a template running against a ball bearing collar, sanded them, stained them, shot them twice with cheap lacquer, and shipped 'em.

Whatdya think?

Better yet, Martin, what do you think?

BOXCAR
  
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08-23-2019, 08:27 AM

Hello Guys

I'm back, sorry to be long to answer. This thread is getting out of hand but in a really good way. Thank you SMT for the ptototyping and testing, it will really save me a ton of beginner's trial and error.

It make a lot of sense that the long radius at the top is continious and do not have any flat surface, I understang that is makes the form a lot easier to build and fit together. I also agree that something around 1/4-5/16 thick should be enough and easier to build.

The more I think about it , I will probably try to build a form and some kind of little flat press with one or two bottle jack to make some trial, may be this winter.

I found some cheap veneer kit that will allow me to make some experiment without breaking the bank.

Guys (SMT and Boxcar) thank you again for your expert experience.

I'll keep you informed of any progress.

Martin
  
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