# Help choosing plywood for table tops - warping?



## Neophyte (Dec 13, 2011)

Friends, I am hoping to get some advice on plywood or other suitable material to build several square bistro table tops for a restaurants of some friends. They will replace the existing table tops. The current tables are made of two sheets of plywood glued together to 1.25" thickness and have pine moulding. Total dimension is 24×24 in. I built prototypes by glueing 3/4 + 1/2 in birch plywood and then trimming them to size (22.5 in per side). I added 3/4 poplar moulding. The problem is that the prototypes are not flat, most of them exhibit some warping. The table tops, by the way, will be painted.
I am looking for recommendations on which material to use, or how to use it. I have thought of trying Baltic birch plywood or a Spanish product called Garnica; glueing so that the grain is perpendicular and so forth. I will appreciate hearing what people know about this topic. 
Marc


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## jonah (May 15, 2009)

If I'm understanding you, the tables will be 22.5" square?

The thing with gluing plywood together for thickness is that once the water in the glue gets into the wood, it swells and warps, and with two pieces trying to move, things get uneven in a hurry.

The solution is a lot of very even clamping pressure and the right amount of glue. Many people use a vacuum press for something like this, just like they would with veneer. There are a few ways to make your own vacuum press, but I've never done it so I can't speak to that.

If a press isn't an option, make sure you use very beefy, very straight cauls and a lot of clamping pressure spread out over the whole top.

An alternative would be to make the tops out of solid wood. That would be a little more work, but it'd be easier to flatten if it did end up warping since you could just take a hand plane to it.


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## woodbutcherbynight (Oct 21, 2011)

Made a mock up for a friends wife for some tables your size. Used 3/4 MDF, glued 5/8 wood flooring to the top and went around the edges with some pine to match the top. Very stable, and even if you had to level it you had real wood on the top.


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## 000 (Dec 9, 2015)

Biggest thing is to have it clamped to a flat surface. 
If it's not flat as it's drying it won't be flat when it's dry.

Has to be clamped up flat…


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## RichT (Oct 14, 2016)

> Biggest thing is to have it clamped to a flat surface.
> If it s not flat as it s drying it won t be flat when it s dry.
> 
> Has to be clamped up flat…
> ...


For sure.

For long term I would think some battens underneath will help with stability as well, and give you something to mount to when you attach it to whatever base you're planning.


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## bondogaposis (Dec 18, 2011)

Tell us about the bases. You should be be able to pull a minor amount of warp out when you attach it to the base.


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## Neophyte (Dec 13, 2011)

> If I m understanding you, the tables will be 22.5" square?
> 
> The thing with gluing plywood together for thickness is that once the water in the glue gets into the wood, it swells and warps, and with two pieces trying to move, things get uneven in a hurry.
> 
> ...


Yes, they are a 22.5" square, then add the moulding. 
This is a great reply. Thanks.


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## Neophyte (Dec 13, 2011)

> Tell us about the bases. You should be be able to pull a minor amount of warp out when you attach it to the base.
> 
> - bondogaposis


They look like this


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## wormil (Nov 19, 2011)

Don't use a Water-based glue, use contact cement or a polyurethane glue.


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## Desert_Woodworker (Jan 28, 2015)

I see that 2 of the finest LJocks have offered their expertise. Here are 2 pics from the net



















Should you decide to clamp the 2 pc of plywood-
For clamping, from the underside use screws.


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## Desert_Woodworker (Jan 28, 2015)

> Tell us about the bases. You should be be able to pull a minor amount of warp out when you attach it to the base.
> 
> - bondogaposis


+1


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## Desert_Woodworker (Jan 28, 2015)

Next question? What is the placement, while gluing, the 2 pc of plywood.
should, 1 pc be placed 90 degrees to the other or not?


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## clin (Sep 3, 2015)

Another option is to screw the two pieces together from the bottom. You'd be able to get a lot more clamping pressure that way than you'd get without using some sort of press.

I also agree with Rick, that contact cement would be a good idea to consider.

I'd also go with 3/4" thick for both pieces. Or use whatever, but have them both the same thickness and same material. I think I'd run the grain of the two pieces (grain of the outside ply of course), in the same direction. That way the inner layers would be glued with grain aligned and the total plies would remain symmetrical. Sort of like the standard odd number of plies, except the inner one would be 2X thick.

Symmetry is important so that whatever happens creates the same forces to cancel out. This is another reason to be sure to finish the top and bottom so that rates of moisture gain and loss will tend to be the same. Though of course table tops get a lot of moisture during use and cleanup.

Certainly Baltic Birch would be very high quality and my experience has been that it tends to be very flat. But a lot depends on how it has been stored. I've only known it to come in 5'x5' sheets, so you'd have some waste. Though you could use two smaller pieces on the bottom where it doesn't show and reduce the waste significantly. But you'd lose much of the strength that way.


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## John Smith_inFL (Dec 15, 2017)

when I make plywood boat transom panels, I find the flattest spot on the floor
I can find, lay down some newspaper, apply a hefty coating of epoxy to both mating 
surfaces. put two drywall screws along one edge to prevent slippage, and apply 
as much weight as I can find and let it sit overnight. (no clamps involved).
cut to shape the next day. I don't cut the panels to shape first and then laminate them.
this eliminates any slippage issues.
the transom panels range in thickness from 1" to 2-1/2" with several pieces of plywood
laminated together. the veneer (if used) is applied after the lamination process.
unless you are making a rocket pad, there is no reason to alternate the grain pattern
in plywood for a 2×2' panel - but it will definitely make it stay flat after it is all said and done.
[with epoxy - there is no issue of transferring moisture to the plywood panels].




























when making transom panels for a boat that will have a 200 pound (or more) outboard motor
hanging on it for years and exerting an enormous amount of stress from all angles, 
you can not afford to have any flex at all. with epoxy as the sealer, it is pretty much
weatherproof from the Bearing Sea to the Equator. so it should be okay for a table top
for you to enjoy your Tea and Crumpets on your patio.

to start with: think outside the box and get away from the mindset of using the finest
"interior plywood and glue" and go to the more extreme EXTERIOR grade plywood and epoxy.
after it is all laminated together, cut to your 22.5" square panels. fill the edge end grain
and any voids with epoxy. after a 24 hour cure, sand smooth, apply your edge banding,
and paint with your choice of exterior paint.

.


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## Tony1212 (Aug 26, 2013)

> Another option is to screw the two pieces together from the bottom. You d be able to get a lot more clamping pressure that way than you d get without using some sort of press.
> 
> - clin


+1

When doing a glue up like this, I would use MDF as the bottom layer and the plywood on top. Then use some drywall screws through the MDF into the plywood. That provides a secure hold and LOTS of clamping pressure. This is how I made my workbench top and tablesaw cart top.

When both sides would be seen, I would put the glue up between two larger plywood sheets on the garage floor and park the front wheel(s) of my car on it. This works very well if there is any cupping in the plywood sheets. Orient them so that the glue up is wider in the center and the edges meet. Then the car will press the center flat.


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## builtinbkyn (Oct 29, 2015)

> Don t use a Water-based glue, use contact cement or a polyurethane glue.
> 
> - Woodknack


That's the way I'd go. Especially the contact cement. No issues with squeeze-out, no clamping necessary and you can use the tops immediately. Oh no screws required either.


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## 000 (Dec 9, 2015)

This is how I would do it.
Make a box that you know will be flat.
cut your pieces oversized.
Yellow glue
screw pieces together from the bottom.
clamp pieces to the flat box.
place clamps around all the edges.
Trim to size when dry.









The yellow glue is going to lock your pieces together so that it wont slip and warp.
The contact cement won't do that.

I would even recommend 3 layers of 1/2" to your client.


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## John Smith_inFL (Dec 15, 2017)

Marc, when I think of "Bistro" I think of an outside patio
where the tables "may" be rained on from time to time.
will your tables ever be exposed to the elements as far as you know ??
that is why I suggested the exterior products and epoxy.
all great suggestions for "inside" tables that will never
see a wet or extremely humid environment.








and where I live, the downtown section of Orlando has DOZENS of 
little Bistros and Pubs with outdoor tables that are exposed to the elements.

.

.


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## builtinbkyn (Oct 29, 2015)

> This is how I would do it.
> Make a box that you know will be flat.
> cut your pieces oversized.
> Yellow glue
> ...


J I know the contact cement won't slip, but you think two equal thickness pieces would warp from the pull of the cement? I know it would if one were thinner. Been there and done that unfortunately.

Really if I we're to make a bistro table and wanted a thicker profile, I'd just build up the edges. 3/4" top is thick enough. Then this would be more easily done.


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## Desert_Woodworker (Jan 28, 2015)

> when I make plywood boat transom panels, I find the flattest spot on the floor
> I can find, lay down some newspaper, apply a hefty coating of epoxy to both mating
> surfaces. put two drywall screws along one edge to prevent slippage, and apply
> as much weight as I can find and let it sit overnight. (no clamps involved).
> ...


this is what I would do in OP's case…


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## 000 (Dec 9, 2015)

> J I know the contact cement won t slip, but you think two equal thickness pieces *would warp from the pull of the cement? * I know it would if one were thinner. Been there and done that unfortunately.
> 
> - builtinbkyn


No, I don't think the contact cement would make it warp.

I think if the wood wanted to warp the "creep" of the contact cement would be enough to let it, whereas the glue wouldn't, Even yellow glue has some creep, best bet would be to use Urea glue, or even epoxy as John mentioned, but IMO, Yellow glue would do the job most economically.


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## wormil (Nov 19, 2011)

> This is how I would do it.
> ...
> The yellow glue is going to lock your pieces together so that it wont slip and warp.
> The contact cement won t do that.
> ...


I suspect the OP just used too much glue but switching to a non-waterbase glue will help. Wood movement is hydraulic and yellow glue has a LOT of water in it. Reduce or remove the moisture, you reduce or remove the warping. I have no idea what you mean by contact cement won't lock the pieces together, of course it will, the plywood isn't going to move. Yellow glue is flexible and will allow allow wood to slip sideways after it hardens, which shouldn't be a problem with plywood except the warping. Any glue is going to be strong enough but reducing the water content will eliminate the need for complicated jigs.


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## 000 (Dec 9, 2015)

> This is how I would do it.
> ...
> The yellow glue is going to lock your pieces together so that it wont slip and warp.
> The contact cement won t do that.
> ...


OK!


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## wormil (Nov 19, 2011)

> This is how I would do it.
> ...
> The yellow glue is going to lock your pieces together so that it wont slip and warp.
> The contact cement won t do that.
> ...


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## TungOil (Jan 16, 2017)

You could just buy Appleply in the proper thickness. It comes in all sorts of thicknesses and is dead flat. Very high quality stuff but not inexpensive. Will save you a lot of labor messing around with laminating tops.

If I were to build up the top from thinner pieces of ply, I would use balanced thicknesses. So, either two pieces of 3/4 or two pieces of 1/2. Don't alternate the grain in this case since the cores are what you want alternating and balanced not the thin veneer face. Vacuum press together with urea-formaldehyde glue on a flat reference surface like the top of a table saw.


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## Desert_Woodworker (Jan 28, 2015)

*Don't alternate the grain in this case since the cores are what you want alternating and balanced not the thin veneer face.*

That is what I was waiting for- thank you

*Vacuum press together with urea-formaldehyde glue on a flat reference surface like the top of a table saw.*

+1 should you have a vac setup.

Also, I just learned about the "fiberglass mat" from above (John) . to me that would change the final dimension, for example from 1.5" to 1.625" would that be a problem?

I just checked out Appleply- *this would be my choice*. They sell it in my area.
Again, thank you-

here is a link to Appleply

https://www.appleply.com/


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## Neophyte (Dec 13, 2011)

> Marc, when I think of "Bistro" I think of an outside patio
> where the tables "may" be rained on from time to time.
> will your tables ever be exposed to the elements as far as you know ??
> that is why I suggested the exterior products and epoxy.
> ...


John, 
I like your idea for its simplicity. 
The tables will be indoors. This particular restaurant opens floor to ceiling windows in the Summer but the tables will not be exposed to the elements. Either way, the tops need to be painted and I will then apply several coats of General Finishes water based poly. The ones I intend to make are replacements for their old (in current use) table tops that I actually painted with BM Advance and then applied the topcoat. The main issue about the table top surface is that it be smooth prior to painting, of course.
Question: Is there a particular epoxy you recommend?
Thanks for your responses and graphics
Marc


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## Neophyte (Dec 13, 2011)

> Another option is to screw the two pieces together from the bottom. You d be able to get a lot more clamping pressure that way than you d get without using some sort of press.
> 
> I also agree with Rick, that contact cement would be a good idea to consider.
> 
> ...


Thanks for your thoughtful response. 
I see the point about finishing top and bottom. My question to you is: 
the table tops will be painted and then covered with GF High Performance water based poly. Would you just use the topcoat on the bottom?
Marc


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## Neophyte (Dec 13, 2011)

> I see that 2 of the finest LJocks have offered their expertise. Here are 2 pics from the net
> 
> 
> 
> ...


Thank you DW,
could you direct me to these posts?
Marc


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## Neophyte (Dec 13, 2011)

> This is how I would do it.
> ...
> The yellow glue is going to lock your pieces together so that it wont slip and warp.
> The contact cement won t do that.
> ...


In my prototypes I used wood glue and you are correct, looking back I think I used too much.
If I understand correctly, glueing different thicknesses of plywood increases warping because one pulls the other 
Thanks
Marc


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## Neophyte (Dec 13, 2011)

> This is how I would do it.
> Make a box that you know will be flat.
> cut your pieces oversized.
> Yellow glue
> ...


Thanks for your response and taking the time to do the graphics
Why would you do 3 layers of 1/2" instead of 2 of 3/4"?
Thanks
Marc


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## wormil (Nov 19, 2011)

> In my prototypes I used wood glue and you are correct, looking back I think I used too much.
> If I understand correctly, glueing different thicknesses of plywood increases warping because one pulls the other
> Thanks
> Marc
> ...


Maybe, working with wood is challenging because it's a natural resource and never perfectly homogenous ... Here is my understanding of wood movement based on college (biology) and 30-some years studying woodworking as a hobbyist … plants move by pushing water from one spot to another. This is well understood. (Plants are fascinating when studied in detail.) Lumber moves much the same way, moisture causes wood to expand, dryness causes it to retract, like a dry sponge if you were ever lucky enough to play with one as a kid. When you added yellow wood glue (which is waterbased) to one side (the center of the glue up) it cause the wood there to expand but the wood on the other side remains the same size, which results in warping. If you eliminate the water, you should eliminate most or all of the movement because petroleum products don't make wood move. Eventually the water level will equalize and if you clamp the boards to a flat reference until they dry, it should return to flat. So I'm not saying that anyone else's solution is wrong, just giving you an alternative. I think some people get attached to their solutions but in woodworking there is often more than one way to skin a cat.

https://thumbs.gfycat.com/AngryNeglectedIcterinewarbler-mobile.mp4


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## 000 (Dec 9, 2015)

> Why would you do 3 layers of 1/2" instead of 2 of 3/4"?
> Thanks
> Marc
> 
> - Neophyte


IDK, I was just trying to sound smart. Plywood always has odd number of layers.
I was comparing that instead of having 1 layer of 3/4" and 1 layer of 1/2" 
2 layers of the same thickness is good.

Rick, 
"I have no idea what you mean by contact cement won t lock the pieces together, of course it will, the plywood isn t going to move."

Your saying that if I were to do a bent radius using plywood, I could use contact cement and because it doesn't slip, there would be no deflection?


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## 000 (Dec 9, 2015)

> Rick:
> 
> "I have no idea what you mean by contact cement won t lock the pieces together, of course it will, the plywood isn t going to move."
> 
> -Rick M,





> Your saying that if I were to do a bent radius using plywood, I could use contact cement and because it doesn t slip, there would be no deflection?
> 
> - jbay


crickets


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## RichT (Oct 14, 2016)

> Rick:
> 
> "I have no idea what you mean by contact cement won t lock the pieces together, of course it will, the plywood isn t going to move."
> 
> ...


Since contact cement never fully hardens, I don't see how it can resist creep for things like bent laminate. I doubt if it's going to matter for two boards glued face-to-face for a table top though. Where are the forces trying to move it?

If I were doing the gluing (new rap lyrics?), I'd use plastic resin glue (recommended here by jbay and Tung) or hide glue. They are easy to work with, strong and won't creep - assuming it matters.

Another glue that has been mentioned, and is sometimes recommended as a low-creep glue is polyurethane glue. Excuse me while I let out a loud groan. I hate that stuff. It's messy, won't come off your skin, and it's weak. In the Fine Woodworking glue test, it came in dead last at only 58% the strength of PVA. I'll be happy if I never see it recommended for anything again.


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## 000 (Dec 9, 2015)

> Rick:
> 
> "I have no idea what you mean by contact cement won t lock the pieces together, of course it will, the plywood isn t going to move."
> 
> ...


I've used some import plywood that might challenge that statement,  
but I agree for the most part. especially 2' x 2'

It's just that 2 people disagreed with me saying that contact will lock the plywood in and I disagree.

I have done plywood bent laminations using contact cement, urea glue, and yellow glue and I can guarantee you contact has more deflection than the other two. No way contact cement locks in the plywood.
(Coming from experience not a stay at the Holiday Inn)


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## wormil (Nov 19, 2011)

> crickets
> 
> - jbay


 I didn't have this thread on my watch list. If in the future you wish to discuss something further and I'm not responding, PM me. I don't keep track of every thread.

This is not a bent lamination but 2 flat sheets, and my solution is for 2 flat sheets. Anything else I say will be repeating myself. It is unnecessary to defend your solution, I never said it was wrong. I'll watch this topic for a few more days if you have anything to add.

As to Rich's point about polyurethane being weaker than yellow glue, it's irrelevant in this situation. I agree it is messy and would not be my choice. I think with less yellow glue it will be fine.


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## RichT (Oct 14, 2016)

> It s just that 2 people disagreed with me saying that contact will lock the plywood in and I disagree.
> 
> - jbay


I agree with you. Like I said, if it doesn't harden how can it not creep?


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## RichT (Oct 14, 2016)

> As to Rich s point about polyurethane being weaker than yellow glue, it s irrelevant in this situation.
> 
> - Woodknack


Glue strength is never irrelevant.


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## Desert_Woodworker (Jan 28, 2015)

Rich- Thanks for the FWW link


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## 000 (Dec 9, 2015)

Rick, the point is that contact cement doesn't lock in 2 pieces of plywood, no matter what your doing.

I'm sure you have your own opinion, so there is no need trying to continue this, feel free to unwatch as I will also.


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## wormil (Nov 19, 2011)

I believe we may be talking past each other. You were referring to flexibility in the contact cement but I meant that the two boards have enough surface area that about any glue (even poly glue) will be strong enough to hold them together. So by using contact cement there shouldn't be any warping.


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## Desert_Woodworker (Jan 28, 2015)

My answer is Titebond 3- reason; the FWW article posted above and from my own personal use. This is my go to glue.









And for composite materials (mdf or particle board) Titebond Melamine wood glue. 









And on a side note-


> (Coming from experience not a stay at the Holiday Inn)
> 
> - jbay


 Seriously, from a stay, at a Motel 6, I learned from their furniture- it was made with pocket hole joinery…


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## Neophyte (Dec 13, 2011)

I very much appreciate the time all of you have taken to contribute to this thread and discuss different points of view. I have learned a lot. 
Thanks!


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## wormil (Nov 19, 2011)

Whatever solution works, I hope to see the final tables and hear how it went.


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## Neophyte (Dec 13, 2011)

Thanks again to all. I may post this question in another forum(s), curious to see what other people have to say.


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## Neophyte (Dec 13, 2011)

If anyone is still following this thread, would you mind giving me examples of resin glue and where to buy? Thanks


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## John Smith_inFL (Dec 15, 2017)

available at all your Big Box Stores and your local hardware store.

.

.


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## TungOil (Jan 16, 2017)

> available at all your Big Box Stores and your local hardware store.
> 
> .
> 
> ...


Make sure it's fresh. Th tech guys at Dap told me no more than 1 year old.


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## Desert_Woodworker (Jan 28, 2015)

> available at all your Big Box Stores and your local hardware store.
> 
> .
> 
> ...


+1 and +1


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## Neophyte (Dec 13, 2011)

I posted an update with pictures of the finished product

http://lumberjocks.com/topics/292177


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