Gina

Photo of Arduino Nano on RPi HAT plus diagram of GPIO pins. The # designations are GPIO numbers.

Redrawn main circuit diagram.

The lathe spares have arrived so I shall probably get the lathe working today. LATER... Replacement layshaft timing pulley and key installed, motor drive timing belt on and lathe working.

+1 for Duet WiFi. Excellent!

Been checking the RPi GPIO lines and have found 7 that can (or do) have pull-up resistors. Since I want 6 that is fine. I shall have to check that any of these have predefined functions that are run on power-up before the code is applied. The 3 remote control lines don't actually need to be pulled up which may be helpful as there are many more GPIO lines that are pull-down. I think the Nano can go on the RPi HAT which would save using a separate stripboard and make connecting easier. It is also safer as it would virtually guarantee that the same Gnd is used for both (as long as I wire up the HAT correctly).

I think this could be the final connection diagram though pins on the Nano may be swapped around to make sensible connection runs.

It might just be the clean one! 🤣

I decided some time ago that a dual print head was far too much trouble.

Initial assignment of Arduino Nano pins. Digital inputs from the 3 push buttons and rain detector, analogue input from Current Sense from motor driver and 2 digital control lines for motor power control.

It's English Electronics Language - province of us Geeks only 🤣

I was originally thinking of connecting the limit switches via Schottky diodes to the RPi, then I did some lateral thinking and realised that if I used analog inputs for the limit switches on the Arduino I could use RPi GPIO lines directly if they were ones with an internal pull-up to 3.3v. The other RPi input from an Arduino digital output will have to use a Schottky diode as logic 1 is +5v on the Arduino.

Personally, I wouldn't advise buying very cheap filament - it can be very variable. I was originally of the opinion, why buy a £40 reel when you can get a £5 cheap Chinese "equivalent". Cheap filament can be very frustrating. You just get your printer nicely set up for the filament you're using when the spool runs out so you go on the the next one of the same make etc. and find you are no longer getting good prints. Stick with one type of filament to start with, such as PLA and learn all the foibles of 3D printers before trying other compounds. PLA is generally considered the easiest to start with - doesn't need as much heat, doesn't produce a horrible stink and is the most environmentally friendly - produced from corn starch and biodegradable. Other thermoplastics are generally made from oil. By far the nastiest filament is ABS. Needs a lot of heat to melt it, a very hot bed and gives off poisonous fumes that you really wouldn't want to be in the same room with. Best of British produced filament and as good as any is "rigid.ink". Also very good and produced in The Netherlands is "colorFabb". This is arguably as good as "rigid.ink" and cheaper, as long as you aren't too bothered about the colour. Their basic ranges are only available in a few colours whilst their full colour ranges are a similar price (or more) as "rigid.ink".

Once you have a 3D printer you can improve and upgrade it. Then when you have more experience you can go on to build your own 3D printers and apply your own better engineering etc. (assuming you're a reasonably competent engineer). A warning though - 3D printers can become addictive! And once you've had one for a while you'll wonder how you ever managed without one. Good luck and I look forward to welcoming you to the 3D printer club.

Just had a very heavy shower and now down to a drizzle. Not much I can do in the observatory anyway until I get the lathe working and the smaller chain pulley made but I can look at the electronics. I'll start again with the block diagram. A lot of the connections are already decided leaving the actual Arduino pins to be decided and the interconnections to the RPi. Taking the RPi first, signals from RPi to Nano comprise Open, Close and Abort. Inputs to the RPi would be limit switches (Open, Closed) and motor current status (Normal, Overload).

Decided to bring the motor unit indoors and take off all the unused bits one of which was a spring pressing on the chain which only added extra friction in this application and made it difficult to feed the chain through.

The lathe parts were sent off yesterday by Royal Mail. They haven't arrived in the post this morning so they should arrive tomorrow. It'll be good to have the lathe working as 3D printing isn't perfect for everything!

I think a pair of ball bearings might be better than a single big one. I could use skateboard bearings or I have several a bit bigger also sealed. Skateboard bearings would be well up to the job.

The larger pulley and original smaller pulley both have a ball bearing and I think I would prefer to have a ball bearing for the new pulley too. A bit more work but not impossible.

The moon is still showing but the clouds are gathering - no imaging tonight.

I shall wait until I have the new smaller chain pulley made before replacing the motor unit on its baseboard. I've scribbled on the pic of the motor drive to show the new pulley and chain run to the spring.

On looking up the properties of Acetal online I see it has a self-lubricating property and is even used in bearings so it would seem that just running on a smooth SS bolt should be alright.

I have a disc of what I think is Acetal, same as I used for the large pulley - 150mm OD x 20mm thick with a 12mm centre hole. I have a 12mm SS bolt it could run on or possibly be turned to take a ball bearing. The outside can be turned to provide a square bottom groove to take the chain. It probably doesn't want to be quite as big as the large pulley and I can turn as much or as little from the outer edge. Cutting the groove would reduce the diameter the chain runs on by half an inch radius, reducing the effective diameter from 6" to 5". I might provide the groove with a chamfer for guiding the chain in better. That would reduce the effective diameter by another half inch.

Lathe spares ordered - total £14.07 - makes more sense that trying to print parts!! They may use stronger plastic - possibly. No sign of metal replacements for the timing pulleys, only change wheel sets. Maybe they consider the timing gears sacrificial in case of a serious overload..

Found the keys £0.68 so I'll get 5 as I'm always losing little things! If I'm careful, I may yet have a usable lathe for non-precision items. Actually, I've discovered the our new neighbours have a Myford lathe so for anything too big or too precision for my little heap I may have an alternative. He doesn't have a 3D printer so some trading may occur in the future 😄

After more searching of AET I've found the plastic timing pulleys - I'll get two - only £4 each. Now I want a replacement key as I can't find the old one.