TOPIC:

eddrick wrote:

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Jonny, where did the tooling come from? - they look like brazed carbide tip tools, & if so, I highly doubt they're getting blunt on plastic (I often grind up cap screws as tooling for machining plastic, & that doesn't dull). 1st off, check how hard the tips are - a file won't even mark carbide, or proper HSS either, unless the files are really posh ones.
More likely, the centre-height setting of the tool is either wrong or not secure - the cutting edge should be a gnats under the centreline of the chuck (Say 0.2-0.5mm). Higher & it won't cut, lower & it will dig in. Best way to check is to take a face cut & see what size the "pip" in the middle ends up. If there's a dimple (No pip) it would suggest the tool is too high. If there's a big pip, the tool is too low. Check the toolholder is rigid/secure. ...

- The blue tooling is 6mm brazed carbide, the bit that went blunt was the one than came with the lathe - a 4mm bit of nondescript metal from the Hu Flung Pu Steel Company The problem is, the lathe is designed with that 4mm bit in mind - ATM I'm using the 6mm bits in the groove on the top of the holder, packed out to bring it to the right height & an impromptu clamp... it's a bit of a lash up until I can work out something better.

eddrick wrote:

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Also, if the various slides have gib-strips (For adjusting clearance/play in the slides), check them to make sure they're tight enough - they should be just loose enough to allow the bits to actually move.

- Yep, did than when building it.

eddrick wrote:

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Having soft stuff out of the chuck is normal, you need to take lighter cuts if it's doing that (Plastics are terrible for it due to the amount of give/creep they exhibit) - I would've thought 0.1-0.3 on the diameter, 0.1 on the face, per cut, would be about right for delrin gears in a tiddly chuck. You can try tightening the chuck more, but you're likely to just squish the part before you stop it coming out. Best stop & check tightness every now & then.

- Yep - been going for a 0.15 cut as the best compromise between speed & low flying work pieces

eddrick wrote:

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Looking at the tailstock ram, are you sure the hole up the middle isn't a morse taper? Beg/steal/borrow a 1MT drill or sleeve - I bet it'd fit...

- Absolutely sure, it's 8mm all the way up. I did see a 3-jaw drill chuck with a 12mmx1mm thread on eBay, that could be a future purchase

eddrick wrote:

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Does the machine have variable spindle speed? If not, see if you can get a speed controller for it, it would make a big difference, especially with plastics (Which need to be cut with slow spindle speed to avoid melting).

- no - it's just what the "12v" (more like 14.4v) transformer that came with it chucks out, all or nothing. I would like something with a soft start, so have been looking at model railway speed controls ... you'd think you could get an old one dirt cheap, but apparently not I've also tried it on an 8.4v Nimh pack ... and discovered why its supplied with a 14.4v PSU - the motor has no torque whatsoever, and like a lot of Japanese car & bike engines, no torque X a gazillion RPM = some horsepower

Non-existant user wrote:

HI!... I'm not a fan of all the plastic on it. I'd rather spend the money and get something like this for a hobby lathe.

www.micromark.c...,9615.html
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Me too But for me it's really a case of have this cheapo tiddler or not have one at all...

Any reason why something like this wouldn't work for speed control?

New chuck arrived very quickly ... had a quick play & it seems to grip a lot better, and be running true

Hazaar for the chuck! Any better?

I can't see any reason why that speed control board wouldn't work, for less than a tenner I'd definately try it, but check what current your motor's drawing under load first - if it's "nearly" the 10A rating, it's likely to run hot &/or be unreliable in a smokey-bangy kind of way. It really wouldn't surprise me if some of the problems you're having are speed related.

Tooling - what about an adaptor-holder thingy, that fits in the toolpost & can hold the bigger tools (At the right height)? OR, do what I do & make them smaller so they fit (Or ask someone nicely to mill them down to size).

Tailstock, 12x1 chuck sounds like a nice simple get around!

The new chuck is definitely better - I had a quick go at facing & reducing the diameter of a bit of nylon 6-6 bar last night & if definitely did a better job - particularly in holding on to the workpiece, nothing went flying. I'm still learning the capabilities of this machine, for example a cut of 0.2 is about right on the diameter, less than that tends to lever the toolholder away rather than cut.

I have a two more of the pukka Unimat 1 joining pieces on order as the Hobbyking copy ones are allowing some rotation on the tailstock & toolholder


I'll have to take so photos of the top bit of the toolholder to try & explain what the problems with it are; currently I'm getting a small outy dimple on end facing.


Re the speed control, I think I'll hold off on that for the time being - ATM I can't get my head around why it'll run off the 14.4v cig packet size transformer it came with, or 7.2 or 8.4v NiMH packs, but not the 12v line on the hotwired PC PSU I use for powering chargers, etc - dang my fuzzy brain

The PSU issue is likely to be a "Switch mode power supply driving inductive loads" problem - I'm guessing the supplied PSU will be a transformer (Is it relatively heavy?) & obviously batteries are a "pure" DC supply. Whereas the ATX PSU has all manner of protection devices looking for anything that might harm a PC motherboard, eg motor related back EMF & spikes. The internal MOSFETs/power transistors won't like any spurious motor-generated "noise" induced into the circuit they're controlling.
The best option for driving the motor will be a proper transformer, or batteries. SMPS powering stuff it's not supposed to, often causes problems, particularly with inductive loads (ie stuff with coils of wire in).

A small "pip" after a face cut is ok, it means the tool is lower than centre height & therefore must be cutting. A big pip means it;s too far below centre height & you risk the tool "digging in" due to the workpiece trying to "ride over" the tool. Aim for a cylindrical pip around 0.5-1mm diameter.

If small cuts can lever the tool away, there's something really not right with the rigidity of the tool holding method... I'm guessing you're winding the cross-slide in to start a cut with the carriage stationary, which always needs more tool pressure than dialling-in a cut depth off the material, then driving the carriage in from the end of the bar with the tool depth preset (Does that make sense?). ie grooves require more pressure than turning a diameter moving along the length.
It's not helping that the material of choice is nylon, which is one of those plastics that tends to "get out of the way" rather than cutting - by the time you've wound on enough pressure to make it cut, the tool is tending to dig in. You really need to try the machine with a bit of free-machining ally ("speedal"), which should teach you a whole lot more of what's possible than confusing you with what's not, based on the particular material's "quirks".
Any soft thermoplastics are a pain - natural polypropylene, black polypropylene, polyethylene, nylon are all a pain, as is annealed ally, copper, anything relatively squidgy really. Harder is usually better. Plastics usually cut better with "soft" tooling, ie HSS or even suitably ground 16.9 capscrews... It usually teases carbide tooling by refusing to cut.
Some materials are a pain with no control over spindle speed too, eg brass, ally (Depending on what speed you're stuck with), stainless, titanium, ABS...

Sorry, distracted myself... what I meant to say was - re the speed control, what wattage & full load current is the motor rated at? - I've got a few "custom/uprated" model railway speed control circuit diagrams kicking about, but they're only rated for around 1A (Toy choo choo power requirements).
You might also find that aftermarket electronic speed controls might need a "coarse" DC supply to make them work (ie output from a proper transformer that has only been half-wave rectified, no smoothing, eg old-style car battery charger), but obviously check the manufacturer's spiel first.
Personally I'd try that one on Ebay, speed controls can be quite expensive, particularly that high rated

The supplied PSU is very light, specs are input 100-250V, 50-60Hz, 1.0A max; output 14.5V 2000mA ... the problem with the PC PSU cutting out was the poor quality plug on the lathe not making contact all the time

Aha, so moving forward again power supply-wise then....
The supplied one sounds like SMPS, being small, light with relatively high output (High input current also gives it away).

What sort of current is the motor using? If it's low enough (Say 1-2A) you could get away with a simple bank of High wattage power resistors (Or car bulbs?) of various values to give you a stepped speed control (Or just a few of the same value, switched to connect them series/parallel to give your different speeds), or even a hefty rheostat, if you can find one.
Still likely to cost more than that speed control though...