Etch Press Build

[JohnHaine]

First and second pics show bearing blocks on smaller press with lift springs. Third shows to and bottom roller - actually on this press the bottom roller is slightly ribbed with circumferential grooves. It's the bottom roller that is driven so it presumably increases the friction. Also the bottom roller is smaller, about 1.5" dia to give better mechanical advantage - another reason to use BMS, you don't want it to bend under the pressure. Top roller is about 3 " dia. I've mounted it on my S7 once to get the rust off and repolish it. 3rd pic shows the platen, the 4th is the side plate of the big Haddon press which dates from late 19th / early 20th century, showing the very crude bearings. It has rollers that are 5 - 6" dia, they are heavy! Both presses have ordinary thread forms, on the smaller press I think it's 1/2" BSW. The handles have roll pins to lock them. You could try Loctite 638, I wouldn't trust Araldite.

I have seen press making threads on the net where they describe making the rollers from a central shaft, say 1" BMS, and an outer drum which could be steel or ali tube; with the spave between filled with for example epoxy / granite chips. If you made accurate end caps to hold the core I think that would be quite successful, though you would need probably to skim the outer surface for exact concentricity.

When you think about this, remember that one of the greatest ever etchers was Rembrandt and I'm sure they didn't have the sorts of machine tools, materials and processes we have in his age!

[JohnHaine]

By the way when you are not using the press you take the pressure off the rollers...if the springs allow.

[Wal]

Hi John,

Thank you kindly for taking the time to photograph and post detailed descriptions of your presses..! Very helpful and much appreciated.

Ok, so bright mild steel looks like it could be a decent way to go in terms of the rollers - certainly expense wise. I'm really surprised to see that EN3B has an elastic modulus over two and a half times greater than 7075-T6. I'd still be surprised if the press managed to bend a 7075 roller - although I probably won't take the chance now that I've seen the numbers..!

I think I'll stick to a thicker platen - the reason being that the bearing blocks are sizeable things - part of the reason I've had to go so big with the rollers (ie. to get them to meet..!) - if I used a thinner plate I'd be operating the press with the top roller near to bottoming out, as it were - a thicker platen will give me a bit of grace in that respect. Sure, I could do that with a bit of wood, plate or what-not - but I like chunky stuff with mass...

...Talking of which - my bearings arrived today. Yep - they're self aligning (old-school, not the dual race sort) - the outer ring has a spherical profile which allows it to rotate into position within the housing:



Right, call me sad - I'm off to read up on Loctite 638..!

Thanks again for your advice and help..!

Wal.

EDIT: Holy Moly - Loctite 276 has a breakaway torque of 60Nm (M10 thread)..! The 270's 33Nm should do me, though...

[Wal]

Hey John (if you're still reading..!)

With regards to the platen - would you size it so that it's full width passed through the rollers, or so that it was slightly wider that the rollers as in the image below..?



Would there be any advantage of milling a couple of shallow grooves on the underside of the platen to enable it to be guided by the support bearings, or does it tend to ride perpendicular to the rollers with the plate/art/blanket in position..?



Wal.

[JohnHaine]

Hil Wal, on the small press the plate slides snugly between the side plates which guide it. On the big one there are stepped rollers rather like the ones you show in your second shot but the platen rests on the shoulder of the step. Trying to machine a groove in a large steel plate is probably best avoided. I don't see any reason why you wouldn't go for the first approach TBH, quick and easy. Most of the plate support comes from the bottom roller, it rests on one of the side plate spacers, which one depends on where it is.

[Wal]

Hello all,

Bit of an update on this (I'll likely post something a bit more comprehensive in the metalwork showcase once properly finished...)



Had the rollers made in EN8 at a local machine shop. Sterling job. Not cheap at £450, but top quality, perfect slide fits into the bearings, great finish etc.

Also had the platen flame-cut and Lumsden ground at a local fabricators. Mild steel, £40 all in. Not sure what to make of it. It's definitely bowed (see pic below) but I haven't been able to get a silver Rizla through the gap (they're around .02mm) - gaps look bigger than they are, I backlit the press with some strong light. I imagine this is something to do with the stock not having been stress relieved prior to grinding... The underside of the plate is working the shoulders of the drive roller a bit, so I might just fit a sheet of 1mm thick vulcanised fibreboard to the underside of the platen. As a material, it's very hard to compress, but should squeeze into that couple of hundredths, I reckon...

[JohnHaine]

Good progress there. The bowing is almost certainly due to the stress relief when the first side was ground. To be frank, I don't know why you bothered to get it ground, since in use you have to put packing under the plate and a felt "blanket" on top, which will take up any small unevenness in the platen. I think the springs are in the wrong place - really you want them to take the weight of the top roller to make it easier to get the plate/blanket sandwich under the roller, then use the screws to apply compression. You have allowed enough space for the plate/blanket?