PRT 4' to 5' Mod?

[gerryv]

Has anyone modified a 4' wide PRT to a 5' wide in order to handle the 5' wide baltic birch plywood sheets? It appears that it would not be too complicated assuming Shopbot would sell the individual components of the gantry at a reasonable price, rather than the whole assembly. The table/base seems very straightforward. I imagine one could expect additional flex in the gantry so I suppose that a lot would depend on how much flex there is in the 4' one to begin with. Mine is a 2006 PRT Alpha.

[bill_lumley]

Hi Gerald , why not just cut the birch sheet in half ;). Way faster and cheaper . Seriously though I wonder how many people buy a 5' machine 'just in case' . You could be in for a long journey to get to 5' and for the extra cost of the machine why not buy some extra plywood . I know I used to think about getting a 5' machine but really only could have used it maybe 5% or less of the time ..... and for those times I just trim a 12" piece off what I am working on . Regards Bill

[myxpykalix]

Gerald,
I have a 2006 prt alpha with a 5x10 table because I have an indexer bay on the X axis to be able to make columns. It would seem to me the only thing you would have to replace is the gantry itself as your rails and all other componnents would work.
I have a custom table so obviously you would have to widen the table but i've never had a shopbot table.

Now the technical experts here could probably tell you the difference in flex between a 4 foot gantry and a 5 foot gantry but it has never been an issue for me.
I guess you have to ask yourself how many times will i need a 5' wide table for cutting and is the extra expense and effort worth it?

[gerryv]

Hi Bill,
I think what it comes down to is when a fella sells off his metal working equipment and sets up a wood shop what's the first thing he focuses on? Well, 1st it's how to turn his Buddy into a part-time metal milling machine, but some good advice from the forum has shown me that I can find the right bits to do aluminum without the milling head. But would be much better with a spindle upgrade of course! Too easy. Hmm, that PRT over there is made of metal; wonder how I can mod. it? All of this is to help my son with his wood shop... right?:o

Hi Jack,
Actually, the idea is to not buy the complete replacement gantry, just the few needed parts that need to be longer. that way I can save enough money to build some belt-drive reducers for the existing steppers... on my modified, I mean upgraded Buddy, heh, heh.

Seriously though, one of the multiples projects being considered for the Shopbot side of the business would require the use of four uncut, 5' wide baltic birch ply sheets per unit.

Guess I'd better start by calling SB to see if they'll sell me the parts.

Has anyone done the width conversion?

[daski]

You could just buy 4x8 Baltic birch.

[MogulTx]

I have only seen the true baltic birch in 5 x 5' segments. (1.5 meters square)

It is sold in 4 x 8??? I have not ever seen it in 4 x 8

Locally, I know cabinet grade (AC or AB) 4 x 8 birch is available, but it is not baltic birch and is less plies and lower quality (inner plies/voids) and I think it is a different glue. ( I have a friend who has done 100's of tables over the years in plywoods of various types- and got a minor education on them at the time)

[feinddj]

Baltic Birch, russian birch, finland birch seems to come in 36 x 48, 36x 60, and all permutations until 60x120. The only issue is what is stocked. I regularly get 48 x 96 sheets. And before you ask North American Plywood Corp. www.naply.com

[ken_rychlik]

My supplier carries the baltic in 4x8, but it is twice as expensive that way for some reason.

[gerryv]

Exactly Ken,
$51 for a 5'x5 vs. $109 for a 4'x8', 13 ply sheet. Not an issue for a few sheets a month vs. the cost of a new or modified machine but if the product does well and the numbers climb, which is what brought me to the question of doing a reasonably lower cost mod.

[ken_rychlik]

I guess thats canadian money because it seems to expensive.

The 1/2 inch (12mm) 5x5's are running 23 for the bb/bb grade

17 dollars if you want a bunch of footballs in em.:rolleyes:

I usually just rip em on the vertical and nest 4x5 sheets.

The one foot drops always seem to find a home. lol

[gerryv]

Yep, you hit it on the head again Kenneth. Although our Canadian dollar is at par with the US greenback right now, the real problem is that our large importers and right on down the distribution chain and even the commercial landlords who rent them space, mostly get away with "excessiveness". Is that a word?

To all,

The grade of Baltic Birch I mentioned the prices on was actually B/BB so admittedly, the price would likely be somewhat higher because of the one clear face, but certainly not by comparison to the prices mentioned above. Here at least, I read that the Finnish stuff is the best (and priciest) and at the other end, there seems to be some questionable stuff showing up that is taking advantage of the unprotected name/term Baltic Birch - thank goodness good Scotch doesn't suffer from the same fate (chuckle).

All of the comments above make a lot of sense of course, so setting aside the pleasure I get from tinkering with the machines as much as their output, the reality is, as I alluded to at the outset, that the specs for this product call for the use of single, 5'x5' sheets rather than pieced together ones.

Thanks to all for the feedback. If I decide to go ahead with this project, I'll post some pic's and test cut results under various loads and conditions when the time comes.

Does anyone happen to know the generic name for the grey coloured rectangular profile that's used in the gantry? Mine (2006 vintage) is the deeper stuff with sharper corner radiuses than the more square stuff that I'm assuming was a bit earlier, but that's a guess. Besides the table/base, it seems that replacing these two profiles, the rack and the two Y tracks with 1' longer pieces are all I would need, plus "maybe" some longer/extended cabling.

Thanks again,
Gerry

[ken_rychlik]

unitstrut was what was on my old prt.

Here is an ebay link to some. Is this what you have?

http://cgi.ebay.com/Unistrut-Channel-Lot-2-Pieces-/220677214153?pt=LH_DefaultDomain_0&hash=item3361630fc9

[bcondon]

I have a full size miller and lathe and I would like to add stepper
motors and use the same software to drive the miller!

Bob Condon