Kids wearing adult clothes~aka 5" mini lathe chuck & more.

Hi, I'm not really convinced that a bigger diameter chuck will have any real detrimental effect of causing harm to a mini lathe. As far as putting extra load on the motor, this should only be during the time it gets up to speed, and once it's up to speed it will act like a flywheel. The danger will be that you can hold a larger diameter in it and if you take heavy cuts on a larger diameter, that will put extra load on the motor. So if you put a big diameter flywheel in the chuck that came with the mini lathe and tried taking heavy cuts it would put more strain on the motor. I might be wrong, but I used the 150mm one in the photo below on my mini lathe, which is about half as much again in weight more than the 80mm one that came with the lathe, and it doesn't make the motor sound any different. The bearings will probably carry more weight than you imagine they would.

Regards Nick.

Hi Nicholas, no I'm not at all surprised that people would do such a thing as I've seen it being done, along with cars towing ahead of me at 70mph on duel carriageways as well as motorways, people towing with their registration number written on a white light-board with a black marker pen or even just written on the tail-board of a trailer with white chalk and trailers with two registration numbers displayed, also seen trailers where their drawbars are pointing badly upwards to the tow-ball and even trailers that look as it they are about to fall to pieces at anytime, no nothing seems to surprise me with the way some people use trailers.

Regards Nick.

Edited By Nicholas Farr on 14/01/2023 09:48:13

Nick, the 4-jaw that you show is quite a slim body version and if I remember them right hollowed out at the back and direct mounting.

The one the OP mentions is not so slim and also has another 15mm or so of backplate thickness to add to the mass that needs to be got moving. Total thickness with backplate is likely to be 70mm or so.

Hi JasonB, yes it is fairly slim body, which in itself is quite light, but the jaws and the fixings are a reasonable weight, but I did have to make a backplate for it to screw onto, to be able to fit it to my mini lathe and in all it weights around 256g whereas the 80mm chuck weights around 146g.

Here's a photo of the back side of the chuck with the Backplate that I made for this and couple of other small screw-on chucks.

Regards Nick.

Edited By Nicholas Farr on 14/01/2023 10:57:29

That chuck looks extremely familiar, my Taiwanese 9x20 came with one, it was for wood use, does each jaw have to be tightened from the rear of the chuck?

Hi Pete, I got this one from one of the traders at one of the exhibitions several years ago. The jaws are positioned via screws from the side and then have to be tightened from behind, and the jaws do not extend beyond the chuck body. See photo in my above post.

Regards Nick.

Edited By Nicholas Farr on 14/01/2023 11:04:53

I'd rather see a driver speeding with a trailer than some of the other stupid things they do. I spotted one while I was refuelling, and asked the driver what was holding the car onto the trailer. He looked at me as if I was mad, and said "the handbrake is on" This was in a motorway service station. Trailers rarely get any maintenance until something breaks - boat trailers are particularly bad for the wheels falling off when the bearings break up - or the ancient tyres finally fail to hold air.

Roof racks are used just as badly; it's not uncommon to find two people reaching out of the car windows to hold a sheet of ply to to the roof.....

Edited By Nicholas Wheeler 1 on 14/01/2023 13:34:05

I have a Chester 7x14 lathe on the bench with it's standard 80mm chuck + a Sanou 100mm 3 jaw SC & Vevor 125mm 4 jaw independant chucks in boxes bought for the Super 7 to hand so, as Mrs B was out, I had a session on the kitchen scales.

80mm 3 jaw as removed from the lathe spindle with jaws 1538 grammes

100mm 3 jaw, no backplate with jaws 2459 grammes

125mm 4 jaw no backplate with jaws 4629 grammes

RDG 125mm cast iron Myford nose backplate 1572 grammes

Likely that a mini lathe backplate would be lighter than a Myford one (no boss) and a 125mm 3 jaw may be a bit lighter than a 4 jaw, but still a 125mm chuck with a backplate could conceivably be 4 times the weight of a standard 80 mm chuck.

A 300mm length of 100mm diameter steel bar (probably larger than you would want to put in a mini lathe, even though it might just fit ! ) comes out as 18.5kg according a steel stockholder online calculator, so maybe 25kg max load shared between 2 bearings and the tailstock. Mini lathes come with 6206 ball bearings as standard (according to Arc Eurotrade's spare parts list) with upgrade options given as 7206B angular contact ball bearings or 30306 taper roller bearings.

What are the specs of load on those ?

My SKF Big Bearing book single bearing ratings for the different bearings are given below. I have converted the kiloNewton ratings given in the book to kilogrammes using 102kg per kN & the numbers are in the order dynamic load, static load & rated speed.

6206 ball bearing 2101 kg / 1142 kg / 15000 rpm

7206B angular contact 2344 kg /1530 kg / 13000 rpm

30306 taper roller 4692 kg / 4488 kg / 11000 rpm

I don't see 25kg or so of 125 mm chuck + backplate + 18.5kg work piece + maching loads generated by a mini lathe really troubling any of the above (or appreciably shortening exected bearing lifespan over an 80mm chuck), particularly as the load will be shared by at least the 2 bearings in the headstock and maybe a tailstock centre as well. Changing the standard ball bearings to taper roller bearings would bring a substantial increase in spindle load carrying capacity if it was felt necessary & non would be troubled speed-wise.

WRT to outside lane towing, I have had the unhappy experience of being side-swiped by trailer that was being towed well in excess of 70 mph in the 3rd lane of a motorway. The trailer was a heavy duty 4 wheel item carrying a mini excavator, being towed by some sort of contractor in a Renault Trafic pickup truck. The driver appeared to have forgotten he was towing, as he failed to allow for the trailer length when he cut if front of me. I managed to avoid being pushed into the truck I was passing and (fortunately) my motorhome remained driveable, but the culprit didn't stop - actually did a runner. Fortunately Mrs B took several phone pics & got his number. Essex Police not interested (incident happened on M11) & never followed it up. £4k damage to my van that the other vehicle's insurer eventually paid out, as the van driver did not respond to their letters about the incident & they took my version of events as being "credible".

Nigel B

Hi, after reading Nigel B's post above, I checked the weights of my two chucks and they should both have an 0 on the end making them 2560g & 1460g respectively.

Regards Nick.

Looking back at Samuels opening post, I can understand the reasoning behind why he has chosen to utilise the SC4 faceplate and standard 3-Jaw 125mm chuck on his mini-lathe.

For what I am about to say, my comments are born out of safety concerns.

The SIEG mini-lathe headstock is designed to support a specific spindle length through ball raced bearings used to support an 80mm chuck, with related expected loads. Similarly, the box section of the headstock casting ‘should be’ 16mm~18mm thick or a little more,.. enough to support ball, angular contact, or taper roller bearings of thickness 16~18mm. To support larger diameter chucks, usually the headstock design should be such that it is longer, to hold a longer spindle, or incorporate angular contact/taper roller bearings to support 100mm chuck, and/or combined with a thicker box section, to support thicker/wider bearings.... all dependent on increase in loads spread over the length of the spindle shaft to obtained better balance and accuracy.

The weight of the mini-lathe castings are therefore designed for light weight hobby use. The positives being that it can be moved easily. If used within its designed limitations, the machine should work fine. When used outside its limitations, probabilities of mechanical and/or electrical failure increase depending on various factors.

ELECTRICAL FAILURES: Below are examples of failure probabilities, based on which version of SIEG mini-lathe this installation is put on:

C2 brushed motor or similar - without overload protection - probability of failure over time > 80%

C2/C3 brushed motor or similar - with overload protection - Probability of failure over time > 60%

SC2/SC3 brushless motor belt drive - with overload protection - Probability of failure over time > 50%

By putting on heavier chucks, you are drawing on more power to drive the chuck. Then if you add heavier stock which you wish to turn, once again requires more power. So again, motor and board will need to work harder. Then there is intermittent load / shock load and power surge (U.K. dirty un-regulated power) to add to the mix.

Note: I am not prepared to give this comparison for competitor brushless versions - most of which have belt and gear drive with high/lo gears. SIEG brushless motor mini-lathes do not have hi/low gears.

MECHANICAL FAILURES: Mini-lathe is designed for use with an 80mm chuck. Higher the weight of chuck, the more the chance of breaking hi/low gears if using a mini-lathe which has such an arrangement. Vibration can increase, and if ball bearings are installed - they will wear quickly. With abnormal loads/shocks, over a prolonged period of time, probabilities of fracture in components/casting can also increase.

I am aware that ARC sells a 100mm backplate and 100mm chuck for use on mini-lathe. This is based on demand, but at the same time, if one considers to make such a modification, ARC would suggest replacing standard ball raced bearings to angular contact ball bearings or tapper roller bearings, if the machine is to be used with a permanent change to 100mm chuck, rather than intermittent use with a 100mm chuck.

Above points relate to machine safety. One should also consider one own personal safety. So if a user decides to consider installation ideas outside the designed limitations, then they need to be aware of issues which can arise, especially from prolonged use of such modifications.

I hope that Samuel has or will consider/keep these issues in mind when using his machine after having made these modifications.

Ketan at ARC

Putting a 5" chuck on one of the small lathes will probably lose 1 1/2" of bed length compared to the standard 80mm. Being able to mount the 100mm four jaw independent directly, minimised my loss of bed length as no adaptor plate was needed

That's the same as what came with mine, they're for wood turning which is why they are much more lightly built, although that aspect probably isn't an issue on a mini lathe.

The problem I had with that type of chuck was that it's incredibly difficult to properly dial something in if you need it to run true, you adjust the screws around the edge, then when you tighten the back screw to pull the jaw against the body it moves it slightly, I found it incredibly frustrating, maybe ok if you're just holding something and machining in one go without removing?

I recently bought a 6" pratt slim body 4 jaw independent for my mini lathe, because it was quite cheap, but when it arrived and I offered it up to the machine to gauge its suitability I came to conclusion it was far too big in my opinion, I also bought a 100mm bison 3 jaw sc, which is the absolute biggest I'd put on there.

One of the strengths of a mini lathe is it can spin pretty fast, by fitting huge 3 jaw chucks you sacrifice this strength.

You need the OD of the chuck body to miss the bed by at least 1" or the advantage of size is wasted. I kept the original 80mm size for the 3 jaw and went to 100mm for the 4 jaw, which are perfect for such a small machine. If I only had one chuck it would always be a 4 jaw independent. It can hold better, and can be dialed in for perfect concentricity or eccentrically. Too many people are too bloody impatient to even bother with them.

A practical issue with large chucks on mini-lathes is that when you open the jaws to hold something big they can hit the bed before reaching the capacity of the chuck.

Neil.

Thank you for all your comments.

Loved the machining old mart, Brill ! ~"Now why didn't i think of that?" saves on the cost & weight of a backplate.

For the record, my mini lathe has taper bearings fitted, Is the geared head version & gearing ratio altered cica 37% lower than standard.

I will use the 5" chuck judiciously, at low speeds.

If i "Goose" something , on my head be it.

Thought i'd give an update for anyone that's interested.

Been using the chuck exclusively for a couple of weeks, no issues thus far.

In fact i'm pretty pleased with it~ only seems to need a light turn of the chuck key to hold things securely.... my smaller 3 jaw sometimes needs a good twist on all three pinions!

I stated the run out was 3 thou.

Dismantled, cleaned & lubed today.

Very little in the way of debris to remove compared to when i've dismantled a new chuck previously.

Re mounted

Using my makeshift 'test bar' plus other non test bars i was pleasantly suprised to get 1 thou run out near jaws & 1 1/2 thou 6 inches from the jaws.

Maybe i'm easily impressed~ but that's pretty good for a cheap ( 'bout sixy quid) Chinese chuck?

Better than you have any right to expect, better than anything i've owned previously.

At the end of the day a scroll chuck is for convienience not accuracy, always a bonus if it get's you close though.