Fastest recommended chuck speed?

[Norris SheldonParticipant @norrissheldon64609]

I have a quite elderly Zyto 3.3 /8 screw cutting lathe in reasonably good condition. The headstock bearings are just plain metal bearings with no play or slop. Top speed at the moment is c600 rpm as measured with a laser tacho. I feel that this is a little slow for some small drilling and finishing cuts, and am thinking of installing a new pulley on the motor and intermediate shaft. What would be the fastest speed I could run at without risking damage to the bearings? I recently cleaned out the oil cups, replaced the felt packing and wicks and top them up each day.

[Norris SheldonParticipant @norrissheldon64609]

[AndyfParticipant @andyf]

I don't know if it's any help, but my elderly Perris lathe (the forerunner of today's baby Cowells) has a hardened spindle running direct in the cast iron headstock, and was designed for a maximum speed of 1,400rpm.

Andy

[Jeff DaymanParticipant @jeffdayman43397]

Hi Norris,

There are two aspects to your question – what speed is safe for your bearings and what speed is safe for your chuck, pulleys and other rotating parts. With large cast iron body chucks there is a danger of bursting them due to centrifugal force. However, this probably will not be a big worry with your relatively small Zyto lathe. When in doubt though, increase speed gradually and stay out of the way while doing so.

For the bearings there is an excellent pocket guide for calculating the PV factor (the main determinor in bearing design) at the following link. It gives max recommended speeds in feet per minute for three kinds of babbit. It would be safest to use the speed number for the lowest grade, as you don't know exactly what grade you have. This number is 800 fpm. To calculate the max rpm at this V value, use their equation V(800 in this case) = (pi/12) x RPM x shaft diameter in inches. Using your spindle dia as shaft dia and solving for RPM will give you some idea of a safe speed.

**LINK**

Hope this info helps.

JD

[joegibParticipant @joegib]

According to the advert reproduced on the Lathes UK 'Zyto' page here:

**LINK**

— the model illustrated had 'split gunmetal bushes' in the headstock. However, given the number of models badged as Zyto (and their various origins) it's probably best to do a physical test.

Norris, if you can access the edge of the bearing shells you could carefully scrape a non-critical area to see whether the bright metal exposed is yellowish or brownish. If so, then the bushes are indeed gunmetal.

Joe

[Jeff DaymanParticipant @jeffdayman43397]

No response from OP yet?

[Norris SheldonParticipant @norrissheldon64609]

Many thanks to everyone who has taken the time to respond to my query. I think I will have a little respect for the old girl and leave her as she is. I have not had a real problem in the years that I have been using it, and I am notoriously lazy when changing belts are concerned, so I would finish up doing all my turning on whichever range I had selected. Bad enough deciding which of three speeds to use without havng two ranges to choose from

Thanks again.

[Author]

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