Etch Press Build

[Doddy]

From an non mechanically-minded perspective, I'd say if the difference between a 1.5mm and a 1.75mm thread is the difference between the thread working or failing, then you're too close to the edge. I'd go with the tooling that you already have, and if you strip the thread use that newly purchased lathe that you just know that you need to turn a tapped steel insert into the newly reamed hole in the ali pressure plate. Or re-make the whole plate from steel.

Preload?, if ease of turning is an issue make a bigger hand wheel - but I doubt that it is. Finer control?, not really much of a difference to worry about.

[Wal]

>I'd go with the tooling that you already have

Heh - well, I have threaded rod in 1.75 and, yep - you've guessed it - taps in 1.5...!

Wal.

[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.