Lathe speed help

[Bill Wilcox]

Hi, I have a piece of dried box elder from the wood pile. It is 5 1/2"X 10".
It is mounted to a faceplate with 1 1/2" wood screws. There are some areas where branches have been cut off and is a bit out of round. I do have a live center in the tail stock.
The lathe is a Craftsman 12X46 running on a 3 hp motor and is secured to the bench well.
Question I have is: The pulley system I have has a slow speed of 856. Is this a safe speed to rough out the outside to get it into balance? If not, then what would be some suggestions.
Thanks

[Kyle Iwamoto]

Wow, 856 RPM? That's faster than the slowest on my Shopsmith. It will be exciting, to say the least. A 3 horse motor? Must be nice.....

Personally I'd be looking for a pulley set to knock that speed down, maybe to 500.... When I turn something out of balance on the SS, it's pretty exciting. And it's only 1 horse. A 3 horse will get that chunk to speed almost immediately.

[Steve Schlumpf]

Bill - that is pretty fast! I have an old Craftsman mono-tube and did manage to turn a number of bowls from rough outs to finish at 875 rpm - it gets very exciting if the piece is out-of-balance! I know there are a number of folks that add an additional pulley to cut the speed down - so that would be one option.

Only other comment - wood screws are not the screw of choice when securing wood to a faceplate. They are to hard and can snap off under force. Recommend using sheet metal screws.

[Bill Wilcox]

OK, thanks for the advice. I thought that 856 was a might fast and it really shakes the table LOL. I do need to change the motor to a 3/4 hp in the OP. The lathe is recommended for a 1/2 hp motor but the 3/4 was what came with the lathe. I will go to the store and pick up a different pulley system.
Exciting isn't the word I was looking for. My pucker factor climbed a few notches when I first turned the lathe on.

[charlie knighton]

when you change to the 3/4 motor ya might want to add some weight to the stand, easiest way is put a shelf and some sand bags

3 horse, 850 rpms wow, ya might want to check your tool rest with xrays for cracks

[Dennis Ford]

If the lathe is not shaking, its not too fast. But since you said the lathe is shaking, you need to balance the wood or slow it down.

[Ryan Baker]

Is that 10" diameter and 5.5 deep, or the other way around?

That speed wouldn't be too high if it were not out of balance. If you can it really round on the band saw first, you might be able to pull it off.

But the short answer is that if the lathe is shaking around, the speed is too high, period. If the pucker factor comes into play, it is also too fast. 856 is too high for a lot of things, so finding a way to slow that down would be useful for a lot of things.

[curtis rosche]

better idea, with that big of a motor, thread the spindle of it, put face plate on it. turn. add VFD to the motor, and you have your self a lathe

[Thomas Canfield]

You might try cutting off any "extra" material to try to imp rove the balance before starting out at such a high speed. I have used a handsaw several times to get rid of extra wood or try to improve balance. I recently purchased some very coarse flap wheels for my angle grinder and would also consider using that combo or fairly recent aquired recip saw bought with that purpose in mind.

[Ryan Baker]

Guys, methinks it's a 3/4 HP motor, not a 3 HP motor. (See post #4).

[Bill Wilcox]

Yes Ryan your correct. the original post said 3hp however it is a typo and couldn't get to it before the second post. I am doing the math now to figure out what size pulley to go look for.
Thanks for all the advice.

[Scott Hackler]

I dont know if you have thought about this but on a blank like that I would mount it on the lathe and with the tool rest close to the wood, I hand spin the wood and use a pencil to draw the diameter. Once I have a complete circle I remove the blank and trim as much as possible with the band saw, chain saw or whatever. The back on the lathe, and make some curlies.

[Paul Atkins]

What Scott said. I really never understood putting on a huge blank that was still square or way off balance and trying to clean it up with gouges. That is what the band saw or chainsaw is for. Anyway, another thing I have done more than once is to loosen the belt enough so it will slip and go slow. Once the thing is balanced, tighten it up. My large lathe has a flat belt which makes it a lot easier, but I have done it with my Delta too.

[Bill Wilcox]

Well I found the formula for figuring out the speed of the different pulleys a person would use.
If your motor runs at 1725 RPM's
If your motor pulley is 1" in Dia.
And your headstock pulley is 4" in Dia
The formula:
1X 1725 / 4= 431.25 RPM's
This is a real good formula that works fast and easy.
So... I was wondering if I put a 5" pulley on the headstock, my RPM's would be 345 RPM's would that be low enough?? Or should I go even larger?
Another question: Is there a site or chart that would show the estimated turning speed for different sizes of stock?
Thanks,
Bill

[Ryan Baker]

It isn't so much about just the size of the blank, but about how well the blank is balanced. If the blank is not well balanced, even 300 RPM is probably going to be too fast on a large blank. A well-balanced very large blank may be able to start significantly higher. The blank will tell you what is too fast -- when things start moving and getting scary. Sometimes even a perfectly round blank may be way out of balance too, because of moisture content, density, etc. Sometimes it is hard to tell until you try it. 345RPM is probably a good compromise in this case.