Teknatool Nova Comet II Electronic Variable Speed Midi Lathe

[Wood Collector]

I m considering buying the Teknatool Nova Comet II Electronic Variable Speed Midi Lathe but was wanting to know if the minimum speed of 250rpm was too fast when starting out of balancebowl blanks that are 250-295mm diameter and 100+mm thick. I would assume thatit would be fine for pen turning due to using the higher speeds. Would it be alrightto have the lathe on a folding work bench or does it need to be on a more solidplatform?
Cheers Pat

[Gabriel]

I don't own one of these, or have variable speed on my midi, but from my experience the speed should be fine for rough turning out of balance stock as long as the lathe is bolted to a VERY sturdy stand.

The only issue of slow speed I have come across (on mu jet 1220 min speed is 500 I think) is that I want to tackle thread chasing but from all I have read, this should be fine at around 100 rpm or slower, so I have to wait til the upgrade. But as per your question, 300 rpm is slow enough for bowls (in my limited experience)

Cheers
Gab

[issatree]

Hi Pat,
To my way of thinking, that is a rather large project for a small Lathe.

Have a look at the BELT that drives the Lathe.

Old Saying : You can Turn small bits in a big Lathe, but you can't Turn Large bits in a small Lathe.
I wood think that you should look for a Larger Lathe.

[Mobyturns]

WC ,


Dale Nish proposed a formula on estimating bowl & platter turning speeds Bowl diameter (in inches) x lathe RPM = 6000 to 9000 i.e. For a 6 “ bowl turn at 1000 to 1500 rpm; a 20” bowl turn between 300 & 450 rpm.


It is a good guide to follow & you will notice that many belt change lathes are not capable of 200 or 300 rpm so it’s a good idea not to turn larger bowls on those lathes at least not as a newbie.


So for your specific example 12" (300 mm) x 500 rpm = 6000 which is OK for a well balanced / behaved blank. 250 rpm should be OK for roughing. No guarantees though with wood. The temptation is to adjust the variable speed to find the "sweet spot" of minimum vibration which is a practice that has both pros & cons. Once you pass through the sweet spot and the vibration starts again it can become very character building. Remember the old road safety message "speed kills".

However as stated above the Nova Comet will be working at its max so every thing you can do to balance the blank before it goes on the lathe and while turning will help - light cuts, etc. I own a Teknatool Mercury the fore runner to the Comet and we have turned bowls of that size outboard on it. It will handle that size - just - but you have to take care and the lathe must be securely mounted to a solid stand - not sitting on one of those aluminium fold up bench / ladders.

IF you are going to be turning 250 - 300 mm bowls often I would recommend finding a larger capacity lathe.

[powderpost]

WC ,Dale Nish proposed a formula on estimating bowl & platter turning speeds Bowl diameter (in inches) x lathe RPM = 6000 to 9000 i.e. For a 6 “ bowl turn at 1000 to 1500 rpm; a 20” bowl turn between 300 & 450 rpm.

How does this work Moby?

Jim

[hughie]

I think speeds and blanks judgements etc are best left to experience. As every blank will vary and formulae wont really fit. Resulting in perhaps a guesstimate.I for for one would be reluctant to use a formula to work out speeds etc, but thats me.

So where does it leave the novice? Several of the chuck makers give max speeds for their equipment and they are conservative so as to keep the turner well with in the perceived margin of safety, this is a good place to start.

But at the end of the day any novice should really get him or herself teamed up with some one of experience anyway they can.

The lathe is a power tool that has lots of potential to do damage and perhaps the fact that they are relatively common and easy to obtain suggests that they are not so dangerous.

But getting back to the question. The lathe in question does seem a little small got a 300 mm blank and certainly the lower speed range is they way to go. But much would depend on the condition of the blank and it species and so on.
As for cutting or chasing a thread, if your new to to it even a 100 can seem daunting. So again good instruction is required too perfect the craft and lots of practice :U

[Mobyturns]

Dale Nish used the formula to give a quick estimate of a safe speed to turn at. Its easier than working out the speed of the bowl at the rim. Using Dale's formula a 12" diameter bowl at his lower limit of 500 rpm is doing about 30 kph at the rim and at 750 rpm the upper limit of his formula its doing about 45 kph. If you were to turn the 12" dia bowl at 2000 rpm it would be doing about 115 kph at the rim. Dales theory is that his recommendations are fast enough to turn efficiently but slow enough to reduce wear on tools and keeps bowl speed within safe limits.

Most turners now turn at far higher speeds than Dale recommends, and that is their call, however as speed increases so does the severity of potential injuries.

[NCPaladin]

I purchased that lathe for my daughter 2+ years ago and it has worked well.
However, you have to take light cuts with an item that large and you want it in balance as much as possible.
Probably the max is usually around 10" (250mm) diameter.
She did turn a couple at 12" on my Nova 1624 and took them back home. Once dry they had warped enough they would not fit on the Comet so just a heads up if you turn green then dry.

I don't think you can just clamp it to a fold up bench for that size work. I took two pieces of stout tube steel about 16" long (400mm), mounted it at the front end of the tube steel, then mounted it to the bench. Mounting at the front the supports go to the rear and are not in the way but still adds rigidity. You could probably do the same and clamp the tube steel to your work bench in order to give it a larger footprint.

At 3/4 hp there is not a lot of oomph at slow speeds. Some other lathes tout 1 HP but also state 6 amp. You can't generate 1 HP with 6 amps by the very definition of HP. IIFC the Comet is 5.7 amp.

If you want to do larger very often I would try to save until you could get the 1624 or another with at least 1.5 HP. The Comet works great at items 9" and smaller.

[Wood Collector]

Just wondering what the best way tostop rust forming when storing a lathe outside in a cover that would stop theweather getting to it. What voltage does the Teknatool Nova Comet II Electronic Variable SpeedMidi Lathe run on?