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pballdan
01-03-2007, 05:16 PM
Well I think I've been convinced to make a mini lathe with a milling attachement for my final project here in the shop before I graduate. I've gotten a small motor from a broken bandsaw, it doesn't have a rating on it but it runs at 1,750 rpm and by the size of it, it looks like it might be 1/4 horse at best. I was hoping to have a foot between centers and a swing of at least 6 inches. Does that sound unreasonable for such a small motor? I do have a 1/2 horse power 3 phase that I could use, but I don't think I would ever have a place to plug it in in my new aparment plus it's really quite large and heavy.

As far as the bed and cross slide goes I think I'll use case hardened rods which the cariage and cross slide will ride on. Would I be better off using the dovetail joint that is normally used on the cross slide?

The school recently scraped an old 3.5 foot south bend lathe which the bed and head was destroyed by students... My boss let me take the threading gear box, which I think I can modify to change the speeds on my lathe giving me a total of 40 speeds. I don't think Im up for adding automatic feed or threading capability unless anyone has some other easy suggestions to make this work.

Any other suggestions or ideas you guys have to help me get started?

pcarpenter
01-03-2007, 05:32 PM
suggestions?...

yeah...get the rest of that South Bend that was trashed. You will be miles ahead with the rigidity of its heavy ways and I would guess the headstock and ways were trashed near the chuck. Lop off the good portion of the rest of the bed and start with that.

Paul

Evan
01-03-2007, 05:39 PM
I can see it now, a SB9 lowered and chopped with Timken rollers in the headstock. Do it right and it would be a spectacular small lathe.

Tin Falcon
01-03-2007, 05:41 PM
Here is one I put together . I did not realy build it Was a NOS lathe with no motor or tooling. Scrounged a treadmill motor and controler. Added a scrounged motor for longitudinal power feed made a couple of face plates. Could give you some Ideas.
go to http://bbs.homeshopmachinist.net/showthread.php?t=19156&highlight=tin+Falcon
For more info and pics.
Tin

pballdan
01-03-2007, 05:42 PM
That would be a wise thing to do, but like I said, the school scrapped it. It is no more :( I managed to convince them to let me keep a few misc parts. Also, when I graduate I will be living in a small apartment with no garage or the like to store a large machine.

hitnmiss
01-03-2007, 06:20 PM
If your ditching threading, why bother with the gearbox?

I'd just use a seperate variable speed DC motor for feed.

Threading is nice to have, though I admit I use it rarely. No substitue when you need it though!

BobWarfield
01-03-2007, 08:21 PM
Variable speed DC motor is the way to go for feeds. Consider putting one on the cross feed too--nice addition that's easily implemented.

RE your ways, I'd be really tempted to find some linear ways on eBay. Your main task then will be to machine a shoulder that is true to mount them against. Likewise, a set of small linears for the cross slide ought to work out well. Cost can be an issue, but I suspect the sizes you want are not necessarily good sizes for folks building router tables, which can cut way down on demand.

Put some T-slots on that cross slide--they're mighty handy for a variety of things. Consider a DC treadmill motor and variable speed control for the spindle. I never have to change a belt since adding that system to my lathe. Less than $100 for both on eBay.

Be aware that things like compounds for various lathes also come up often on eBay, or maybe you can borrow one from the scrapped SB lathe at school.

I would consider making this beast from aluminum rather than cast iron or steel--less warpage there. Evan can extol the virtues on why he is building his mill from Al, and there have been many others who have gone down that path.

Alternatively, I'd use DOM tubing with a flat plate welded atop for the linear slide guides. Surprising rigidity for little cost and effort. Fill the tubes with sand or concrete. There is a great article on this in an MIT PhD thesis available on the web. I've lost track of it, but the guy's name is Bamberg and he designed a 5-axis cnc tool grinder based on these principles that is now a commercial product.

Lastly, think about how to get clever with the spindle. For a small lathe like this, collets would be really cool. I wonder if there is a ready made collet gadget that can be turned into a spindle with appropriate machining: A spin index or some such might be a viable donor.

I have a list of lathe mods on my web site that may yield useful information for you to think about on your project:

http://www.thewarfields.com/MT/MTLatheMods.htm

Keep us posted on your ideas and progress. Should be a lot of fun!

Best,

BW

pballdan
01-04-2007, 04:58 PM
Well, i've done a bit more thinking and I've decided to make my spindle accept 5C collets so I can use this:

http://www1.mscdirect.com/CGI/NNSRIT?PMAKA=GA09670548

Does anyone know how large in diameter the throw on my lathe will need to be to accomodate this when it is expanded fully?

Evan
01-04-2007, 05:16 PM
You will need about 6" swing (3" from centerline) to handle a 4" chuck.

I would plan on fastening the chuck to the spindle, either threaded or other means. Collets are't designed to handle work larger than the holding diameter of the collet. If you try to turn large work with a chuck held by a collet taper there is a good chance of it slipping.

Tin Falcon
01-04-2007, 05:37 PM
Dan:
The chuck is 4"" so each jaw is approx 2" long. My rule of thumb is not to extend the jaws past 1/2 of there length. that would require at least a 6" swing on the lathe. Keep in mind the higher you place the center the stiffer and heavier the bed will need to be. a 6" to 7" swing is still relativly small . For example a 3 1/2 x 17 sherline weighs 30 pounds.A 7x 12 import weighs 80 pounds.
I like the Idea of using a spindle that will handle 5-C Collets that meanns you can put a 1" piece through your head stock nice hope it works out for you. Also 5-C is available in hex and square.
Tin