Etch Press Build

[JohnHaine]

Wal, I've worked on 2 etching presses for my wife, and I think you are overthinking this. One is a small tabletop one, the other a beast weighing the best part of half a ton that sits on a stand on the floor.

Neither has anything very fancy in the way of bearings, just a u-shaped recess in a lump of steel or iron that a spigot on the end of the roller sits in. On the tabletop press I made a nice pair of CI blocks bored out to fit the spigots that slide on the edges of the slots in the sides, mainly so I could lift the roller using some springs to make it easier to manage, but the previous ones were just brass blocks with the u-shaped cutouts.

There needs to be a steel platen between the rollers that gets wound across supporting the plate and paper. On the smaller press this is 1/8 inch bit of mild steel plate, on the big one its 3/4 inch by 18 inches by 3 ft or so, a real brute.

You absolutely don't need any fancy thread on the pressure screws, an ordinary coarse metric thread would be fine. It doesn't get much use, the pressure isn't very great. Remember that there will be a felt blanket between the rollers and the paper that regulates the pressure and takes up any unevenness.

I'll try to take some photos for you and post them here, any questions just ask.

[JohnHaine]

By the way neither press had the springs originally. I added them to the smaller ones to make it easier for my wife to get stuff between the rollers by reducing the top weight. The big one, which has VERY heavy rollers, doesn't have them but it's still manageable. When you put the plate + paper + blanket on the platen you then have to get it between the rollers and as you can imagine it can get a bit hard to turn the handle.

[Wal]

Hi John,

Excellent stuff. Would be great to see a couple of pics of what you've built.

The bearings and blocks I've gone for are pretty cheap and easy to come by and what with readily available CAD files it makes the designing that bit more straightforward: just need a correctly sized slot and a bunch of holes drilled in the right places on each of the walls and it should be good..!

Yep - after the initial faff, I'm going with a standard coarse M12 for the pressure adjustment spindles - I finished up the knobs for these earlier (pics below) - they're also threaded and I'll likely use a strong epoxy to hold 'em captive - or a grub-screw - or a nut... will decide when I get there..!



The biggest issue I've come across are the rollers themselves. I've looked at conveyor belt spares (not much in the way of live axle, no Ø80mm options and they all seem a bit flimsy), replacement parts for commercial presses (well expensive), fabricating them myself out of tube stock / steel bar etc. (too ramshackle). I'm pretty much committed to having 'em turned, which will cost, but I'm keen to get it right..! Right now I'm thinking of 7075-T6 for the bottom roller (suggested as it minimises the effects of cold-working/distorting the steel plate over time - yes, yes - a RIDICULOUS consideration for the use this will get, but have a read about it here) - and a mild steel top roller - but what grade of mild steel..?

Yep - I'm aware of the plate - it's in my 3D model, just rendered with a bit of transparency. I'll use a steel plate (again, any suggestions on a suitable grade?) - 8mm thick, ideally stress-relieved and ground parallel. Yes, yes - RIDICULOUS...

As you can see, I'm probably over-doing this - but you know, why not..?!

Wal.

[JohnHaine]

Our small press uses BMS for both rollers - much cheaper. Some increase in weight I guess. I'd have concerns about the lower roller bending if it's ali. The main constraint on BMS type is probably machineability - a FC type would turn better.

Regarding bearings - beware using roller bearings unless you can rely on the rollers remaining aligned. The crude open cradle type are very tolerant. You can get self-aligning ball bearings.

Plate - really it doesn't matter! Since the part that does all the work is under compression from top and bottom rollers, which will also tend to straighten out any lateral bend, you could use aluminium sheet or BMS plate. If you use the latter, probably any of the laser cutting suppliers that for example supply laser cut loco frames would cut you a piece which would have clean edges and not be buckled. 1/8" would be plenty think enough. The main thing is to make sure it's smooth with no nicks or dings.

[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...