Etch Press Build

[Doddy]

Ah, one of those classic Homer moments. Doh!

[m_c]

Generally in softer materials, bigger pitch is better.

For this kind of application though, some form of square/acme thread would probably be a more suitable application, but that can get expensive.
I think I'd personally go for finer, rather than courser, as the forces aren't going to be that big in the grand scheme of things. If it does strip, either remake the top bars in steel, or put a helicoil in the aluminium.

[Wal]

Good call on the ACME - the thought had crossed my mind, but I just assumed too expensive and a bit more of a hassle to come by. My assumption regarding the expense was wrong:

https://www.ebay.co.uk/itm/1-2-10-AC...-/382095182523

- that's about half the price of 1m of 1.5 pitch high tensile threaded rod - and I only need around 12", and this tap seems like good value:

https://www.ebay.co.uk/i/35213872052...7750313&crdt=0

If you dig a bit deeper, though, you'll see the rod's readily available in metric, but the taps aren't... Or if they are then they're a couple of hundred quid..!

Right, I'm faffing now. I've ordered a coarse 12mm tap (not in ignorance of your suggestion m_c - I looked at what I already had and what was going to give me the least amount of ball-ache going forward..) - I'll try it. If it's shite then I'll remake it so it's not shite. 👍

Wal.

[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!