need machinists advice

We have a lathe at work that I play with once in a while but I am nowhere close to being a machinist. I have to turn something that I don't want to mess up so I could use some advice on the set up. I'm going to be turning a belt pulley that's roughly 12.5 inches in diameter. How fast should I run it?
 
What material are we dealing with? With that
diameter, I'd say run it as slow as the machine
will go, that's a lot of feet per minute
 
All I can say for sure is that I torch tested a spot and it appears to be some type of cast iron. Not very hard. I used a burr to gouge out a crack prior to welding and it cut like butter.
 
(reply to post at 01:39:25 03/14/14)

It's all in the material, and the cutting tool. High speed steel tools will have a much slower cutting speed than carbide.

I do 99% of my work with carbide, if the pulley is cast iron and that diameter I'd try my 140 rpm setting. In that range od speeds I've got a 350, 260, 190, 140 RPM speed, 350 would burn the tool up, 190 would work well.

A good rule of thumb is XXX surface feet per minute. Just say that pulley is 12.5" Diameter, 450 surface feet per minute for the material involved and the speed would be close to the 140 RPM setting I have on my lathe.
 
you can spin it fast or slow to cut cast iron. just do a test spot, sharp bit, make sure your straight in the chuck. its kinda trial n error for first few mins. youll be fine, just take your time.
 
depends on how much your chucking on, how rough the surface is and if there is any interupted cuts, what kind of cutting tool you have. If I had plenty to chuck on, I would probably run a little faster than 60 rpm, maybe more like a 100, because when the diameter is big a little momentum can help keep chatter down. Just make sure your first cut gets beneath the scale of the cast iron
 
Safety is your #1 priority here. Manually operated lathes are probably the most dangerous machine tools in any shop. That being said you want as rigid of a setup as possible. Are you using a carbide inserted tool or High speed steel? Machinists go by Surface footage on the cutting tool charts. General SF for HSS is 60-100 for low carbon steels & cast irons. Carbide can be run 2-3 times faster. To convert SF to rpms take SF/.262/Dia of tool or workpiece. 60 rpms on a 12.5 dia is 196 SF.
 
Thanks guys. I started slow (75 rpm) to knock down the spot I built up, and then I went up to 158 to finish it off. The top came out nice but when I trued up the inside I found three little hairline cracks, beneath the area I built up so I have to decide how to go about fixing them. Now that the pulley is trued up on the outside I'd hate to warp it with another heating sequence. All of the guys in the shop don't think they'd ever be a problem at the low rpm's that it'll be turning but I don't know if I can get used to the idea of having cracks in something spinning so close to my right foot.
 
Thanks for asking a legitimate question. Its a shame that a
legitimate question only gets six replies. Makes you wonder
where all the expert machinist are doesnt it
 
(quoted from post at 03:39:55 03/15/14) Thanks for asking a legitimate question. Its a shame that a
legitimate question only gets six replies. Makes you wonder
where all the expert machinist are doesnt it
While I was working on my project during my lunch break I was looking around our shop and seeing all of these great tools that never get used. The lathe, a mill that will do verticle and horizontal, a big trip hammer, forge, etc, etc and thinking what a shame it was that we didn't have any guys that really know how to run them anymore. Just then my boss came through and told me to get back to the lunch table, take as long as I wanted on my project and to consider it on the job training. Pretty cool of him.
 
(reply to post at 05:58:49 03/15/14)

Get a "machinists handbook". Several are available and maybe one of the guys will just give you one. Read it in your spare time and just rember the basics, that a carbide tool will cut XXX feet per minute, a high speed steel tool will cut XX feet per minute, steel, cast, alumnium.

A little common sense and you'll be well on your way and be able to play around on the machines.

You'll try and cut something to fast, burn the tool up and rember the simple rules.

I've got all CNC machines alright.......crank n crank. It's nothing fancey but I can sure do a lot of stuff with the basics.
 
(quoted from post at 19:39:55 03/14/14) Thanks for asking a legitimate question. Its a shame that a
legitimate question only gets six replies. Makes you wonder
where all the expert machinist are doesnt it


Yeah, because your expert response was backed up by showing the math on how to figure out surface feet per minute and referring to validated charts such as those published in the machinists handbook.


Get a life troll. The previous responses were 100 x more valuable than the two bits you posted. Some expert you are.
 

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