New Lead Screw for Kodak/Century Bi-post Stand

The lead screw for my Kodak bi-post stand is very worn, and the nut wouldn’t travel over the length of the screw. I brought the parts to one of my wife’s uncles. He has over 50 years experience using a lathe, and he has a commercial one in his workshop. By tapping the nut very lightly with a small brass hammer, he was able to reform the grooves of the rod. The problem was the worn area, as any racking of the nut caused a misalignment, even with careful hand-turning. That didn’t bode well for tilting the table with the hand crank.

To replace the old ½”, 5-start, 20 tpi screw, I bought the following parts from Ebay user imsrv:

304033-1 1 qty 1/2-10 x 12 inch 2 start RH Acme threaded rod $8.95 (sale price)
304038 2 qty, Shaft Collar (Clamp) 1/2-10 acme 2 start $6.99 * 2 = $13.88
304020-del-nut 1 qty, 1/2-10 Acme Delrin Nut Block Rt Hand. 2-start $12.00
304330 1 qty, Flanged Bearing ( 2 pack ) 1/2 ID, Dual shield for No-Machine leadscrew assembly. Steel $8.30

Total $43.13 plus shipping

I bought the bearings and shaft collars as I thought that I would have to fabricate new mounting hardware. Luckily, I didn’t need them. Uncle Ambrose cut down the Acme rod, turned down the ends to ⅜”, and threaded the handle end ⅜-16. The grooves of the thread were deep enough that turning down the rod didn’t completely eliminate them, but the grooves are very shallow and smooth. They shouldn’t be a problem. The machined rod slips right in to the old mounting parts.

The delrin nut is just slightly less wide than the wooden shaft of the table’s tilt mechanism, but it’s close enough that using two pieces of flat aluminum bolt through the nut make a good connection. I’ll round the corners on one end of the pieces, clean them up, and paint them black.

The updated mechanism works very well. It takes 5 turns to move the nut an inch, as opposed to the 4 turns required by the older parts, but that isn’t a problem in use.

I hope this info helps out people trying to get their Kodak bi-post stand in working order.

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Holy *** ! Mine are both gone, and I have talked to two other forum members with the same problem!

You are a saint, Peter. Thank you for the great information.

Jac

Glad to help, Jac.

Congratulations on a nice job.

Before someone feels compelled to chime in and say that a piece of building-supply-center threaded rod will work just as well, let me point out that you have preserved a valuable feature of the original design: the increase in operating speed is obtained at the expense of mechanical advantage, which may keep you (or someone less meticulous) from breaking the thing when it reaches one end of the travel!

Great job Peter!

Thanks, Randy. It's looking better now that I've rounded the corners on the aluminum pieces, sanded and cleaned them up, and painted them black. The mechanism is very smooth, and it stays in place. The entire travel of the screw can be used, including a bit of up-tilt, although I'm not sure why anyone would use that. There's no problem with going too far. If there was, I'd have used ring clamps to limit the movement.

Tip down can be handy.


I have the same parts to use as focus conversion on 8X10 Tailboard Century.

I look forward to seeing the conversion.

If I didn't want to use the old hardware, having the ends turned down wouldn't have been necessary. The stock Acme rod taps snugly into the flanged bearings.