I picked up a few machines.

G

Geerbangr

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First off I'd like to say hello to all. I have zero experience operating a metal lathe and a mill. I play around with cars in my shop and always need something machined in one fashion or another. I have a friend I kinda rely on that helps with some things for me but like everyone else I get tired of asking him to do things for me.

So after watching Craigslist for a while and opting out of buying anything from HF I found these two machines.

OTMT OT252700

27.5" belt lathe

Enco 20" mill/drill

These machines are supposedly brand new.

I started cleaning the lathe up first. It appears to be in nice condition. It was still covered in cosmoline I guess. I can post a picture of my lathe and then maybe start asking questions I have about operating it with success. If anyone has experience with one of these elcheapo lathes like mine and have corrected any issues the lathe comes with please feel free to share with me.

IMG_0158.JPG
 
So I have some questions I'm wondering about with this lathe. It came with a stack of spare gears and zero tooling nor a manual.

Everything seems to work well on it that I've tried. Different speeds, carriage runs manually and auto feed. I don't not see a way to reverse the lathe.

I've waded through YouTube videos looking for some answers on how and what with to get started using this machine. Tooling seems to be preferential to ines personal taste. What would be decent cutting bits to purchase for a beginner? I'm not looking for bits to cut parts for the space shuttle, just bits to get started learning how to properly use the machine.

The other thing that eats at me is the backlash in a few of the controls. Some of the videos I've watched claims backlash to be inevitable in lathes due to tight tolerance causing the machine to bind up. How much backlash is too much and how much is not enough? I do understand it is a low level machine so maybe I'm being to picky.
 
To start here's a link to the manual. http://www.otmtmachines.com/images/manuals/87-115-949.pdf

The gears are most likely your threading gears.

With regards to backlash, all machines will have backlash. Depending on the types of screws and thrust bearings, some will have more others will have less. Acme threads typically used on manual machines will have more than the ball screws typically used on CNC machines. For example my manual lathe has ~0.005" backlash on the cross-slide. I can adjust it by tightening the split nut and and the nuts on the lead screw. But as I tighten them up the friction to turn the lead screw also goes up along with the wear on the screw and nut. So it's a balance. Accuracy while machining is maintained, by always machining (cutting) in the same direction (in or out, right or left) as you were when you set the zero on you dial.

There are some good YouTube video that show how to work with backlash, much better than I can describe with words.

Here's an example of just one of them:

As for lathe cutting bits, you could go with a pre-ground set of HSS bits. HSS works better with lower power machines. Pre-ground will get you started with bits ready to cut, while they can be resharpened on a bench grinder. There are also soldered carbide and insert carbide bits. Little Machine Shop and Grizzly Industrial both have some less expensive sets that are good for starting out.

Hoped this helped.

Continue to ask away, there are lots of talented machinist on this site that will be happy to answer your questions.
 
Hi @Geerbangr,

Welcome to the site!

That lathe is about 3 times bigger than my first metal lathe (Sears/Atlas 109).....and looks to be in much better condition too.

For cutting bits, I use almost exclusively HSS and sharpen them myself.
It is a personal choice, and there are some great discussions here:
http://hobby-machinist.com/threads/lathe-cutting-tools.59874/
http://www.hobby-machinist.com/threads/how-to-grind-a-hss-turning-tool.52581/

It might not have reverse, many hobby-level machines do not.
If in does have reverse and the chuck mounts on a threaded spindle nose, be careful, it could unscrew during use and ruin your day!

Be safe and have fun!

-brino
 
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I think I'll get started with hss bits. So the maximum tool size for my machine says 1/2". Would it be fair to say that 3/8" bits would be the best all around size to use?
 
Another question of concern. My tool post has 3 bolts down each side. That let's me set up 2 bits at on time, correct? That way when one bit dulls I can rotate the tool post and resume working with the other bit, correct?

Also, is it common practice to utilize all three bolts to hold the bit tight? With that knowledge I can figure out how short of a bit I can use. My plan is to run hss bits.
 
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You can fit four tools in the tool post at once. This is so you can have four different tools set at the same time. Tool height is important. The cutting edge needs to be at the centerline of the work. With that type of tool post, you adjust the height with shims underneath the bit. Using 3/8 rather than 1/2 would mean adding an extra 1/8" of shim under the tool. And you will quickly learn why we spend multi-hundred dollars on quick change tool posts.
 
RandyWilson said:
You can fit four tools in the tool post at once. This is so you can have four different tools set at the same time. Tool height is important. The cutting edge needs to be at the centerline of the work. With that type of tool post, you adjust the height with shims underneath the bit. Using 3/8 rather than 1/2 would mean adding an extra 1/8" of shim under the tool. And you will quickly learn why we spend multi-hundred dollars on quick change tool posts.
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I think reading between the lines it's not s good idea to use shims under a bit? Does a quick change post always keep the bit on the centerline of the work piece?

Would a wise investment be to purchase a quick change tool post? Is so which quick change would be suitable for my machine?
 
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