anyone converted a Sherline / desktop lathe/mill to CNC ?

Agreed. What I find is that many folks think CNC will make make up for not having machining skills, but this is plainly not the case. You need as much -- if not more -- skill to run a CNC rig than running a lathe or mill manually. The only real difference in the CNC makes part making fairly repeatable. You still must understand the physical properties of the material being cut, the affect of feed rates, spindle speeds, cutting depths, tooling and tooling angles, etc. You must still understand tolerances, how to draw out and measure parts, and everything else that goes with traditional machining. CNC makes none of this go away.

I always recommend first getting a standard lathe or mill that can be upgraded to CNC. Spend a few years learning how to use it, and *then* convert to CNC. (I guess you could shorten it to months, if you practice more or less full time on it.) Otherwise, the learning curve to acquire machining basics *and* CNC skills is quite formidable. Time and again I've seen he usual result is discouragement. More tools in the garage that don't see much use. And these are fairly pricey for that.

-- Gordon

I have used both big and small machines. I don't think the accuracy is much different, but acheiving that accuracy requires more skill and patience on a small machine. But it is still much better to start with a small machine, because it will help you develop that skill. A Sherline is small enough for you to feel the vibrations as you cut into a piece of metal. You are close enough to smell an overheating bit. You will get a good intuitive feeling for how to cut different materials. You will be able to tell when a bit is too dull just by listening to it cut. You will become a better machinist than someone who has only used big machines.

Shortly after you buy the mill, you will find you also need a rotary table. So you may want to go ahead and buy them together and save on shipping.

Some other advice: Don't think of these as just metalworking tools, they are also great for plastic. When I need to machine a robot part, I probably use acrylic or acetal (Delrin) 80% of the time. Acteal is very easy to machine, and is quite rigid and strong, but not as cheap as acrylic.

machines? Is the

Plastic is a large part of what I want to do with a min-mill/lathe, too.

up for

You need

lathe or

making

The repeatability is the only reason I want to look into adding on CNC capability sometime in the future. I've done enough programming to know that sometimes a good old fashioned pencil and paper is a lot faster than any spreadsheet or CAD program!

Since I bought my drill press a few months ago, I have realized that it is not the precision tool I thought it was - just a lot better than my cordless drill. I'm finding that the most fun I am having ( now that I am into scratch-built robotics ) is the physical stuff - the nuts & volts and metal & drilling. So the lathe / mill comes into play so I can make smaller parts more precisely ... and *mostly* just because I *want* to !

Well, just had to yak it up a bit ... JCD

Unless it's a real crap drill press, it will be about as "accurate" as the typical desktop mill. In fact, a mill is just a drill press with some refinements. "Accuracy" isn't always one of those refinements!

For under $100 you can retrofit a Harbor Freight bench drill press to work as a just-passable poor-person's mill. It'll be good enough as a learning tool. You need a basic XY slide, which you will bolt to the base of the drill press. Harbor Freight sells one or two...get the better one, or opt for a model that doesn't exhibit the backlash as theirs do. Try to find a collet holder for the chuck, and invest in a couple of real milling bits. Drill bits are too long and too flexible. You'd be surprised what you can put make after a bit of practice. Start first with some softer materials.

I'm finding that the most fun I am

Absolutely, but as I mentioned CNC is in many ways harder to master than manual machining. I think you're on the right track if you look for a CNC-ready machine, then make that plunge after having built a few miniature steam engines with the thing.

-- Gordon

Fur lurkers: Acetal really stinks if you overheat it (it's the formaldehyde releasing), so make sure the bit is sharp.

For Bob: I personally like high density polyethylene. Cuts and mills like butta, and doesn't release so much smelly stuff. About as durable as acetal, but maybe not as dimenstionally stable. You can buy a cheap kitchen cutting board to play with it before purchasing a larger sheet from the local plastics outfit.

-- Gordon

Whole new world. Plastics requires very specific adjustment of spindle and feed speeds, or else the plastic gets overheated, gumming up the tooling, releasing toxic fumes (if the plastic melts or burns), and producing extremely out-of-tolerance parts because of expansion. In fact, plastic expands quite a bit even if you're careful, so you need to take this into consideration when producing the part. The expansion changes depending on the type of plastic, amount of cutting, and its cubic size.

In some ways, working with plastic is harder than aluminum -- first hand experience here. Learn on one of the softer alum alloys first.

-- Gordon

Gordon,

Where would you go looking for surplus plastics and metals for robotics?

Thanks

TMT Gord> > Some other advice: Don't think of these

"accurate" as

with

refinements!

Wow - I didn't realize that. The inaccuracy I experience could well be from my lack of skills in this department. Mostly, I find that the drill bits wander a little from where I mark to begin the drilling.

The drill press I have is a $100 Craftsman.

press to

I keep thinking this may be the best way to go, too. I bought a X-Y machinists vise and although it looks good and well built, the movement on it is less than smooth. Got if off eBay so I was prepared for the get-what-you-pay-for effect. No big surprise. I'm sure a real X-Y slide would be better anyway since it would provide more ways to clamp something down.

flexible.

I just read what you wrote about drill bits being flexible! Duhh! I think that is a large part of my problem. I am definitely going to read up on this some more and see what I come with. Perhaps by that time my "fever" will have gone down some and I will listen more to my bank account than my "fever for a new toy"! :-)

Thanks Gordon! Always good advice from you. James C. Deen

Because most of the work I do now is for resale wioth Budget Robotics, I don't use surplus. For plastics, it's far better to buy new sheets anyway, as you get a consistent quality, and the price (for the kinds of materials I use, such as PVC, HDPE, and ABS) is reasonable. Most areas have a plastics distributor that offer these by the sheet. (My CNC router also needs sheets in specific sizes, so I can't use odd cutoffs.)

For metal I used to buy the wrought iron from welding outfits. It's pretty cheap. The aluminum channel stock I've always gotten either from the hardware/home improvement store, or for as-milled alloy a local metal surplus outfit. Down in San Diego we have K Street Surplus, plus a bunch of others. We also have a major Navy shipbuilding presence, so you can imagine surplus metal is not too far away...

-- Gordon

Absolutely. This is from a combination of having the wrong point on the bit, no starting punch mark, and perhaps even the surface shape of the part (rounds tend to cause more walking around that flats).

There are a couple books you may want to look into, and most are older so they should be at the library. One that's pretty good for beginners is is Home Machinist's Handbook (Briney). It's about half pictures and half text, and is not bad as a beginner's book. The other is Joe Martin's Tabletop Machining. As he owns Sherline it's Sherline-centric, but much of the information applies to most any tabletop machine you might have. I found he jumps around a bit, but just about all the info you'd want is in there.

Check out Reid Tool & Supply for some decent end milling bits, in different sizes, shank lengths, and point styles. For practice you'll want 2-flute square end. Diameter shouldn't be less than 1/8"; 3/16" is even better for playing around.

Of course, eye protection is the most important tool you have in your garage. It takes all of a split second for some aluminum sliver to get into your eye, but several hours at the hospital to remove it before it scratches the hell out of your cornea.

-- Gordon

Hi,

The real problem with trying to do this, is that most drill presses hold the chuck into the spindle using a taper. Lateral (i.e. sideways) pressure will cause the taper to loosen, and now you have a spinning chuck with an endmill on it, potentially flying around.

In order to safely use a drill press as a mill, you really need a drawbolt or something similar to secure the chuck to the spindle.

Obviously, if you're using a drill mill, then it will have the requisite drawbolt, but a regular drill press doesn't

Dave Hylands

beginners

pictures and

Sherline-centric,

I just got Martin's book in the mail from Amazon. It looks like one I will read & flip through, then read and flip thru some more when I *really* understand what he is talking about. Kinda like yours! :)

you'll

Will do. Thanks for the tip on Reid Tool & Supply.

to get

before it

This is one thing I *do* know. With age/experience has come the realization that even mundane chores can throw a sliver of something bad into your eyes. The scariest and the one that really made me realize this was when I was tinning the end of wire with some solder one day - pressing it against the wire - the solder slipped off & the wire flung a tiny bit right into the corner of my eye! It scared me so much I'm not even sure I felt the heat. So now I always wear glasses for that and a few other things I used to skip protection for.

And of course, I have verified for myself that one needs to clamp down metal work when using ANY kind of saw or high speed device - not just hold it by hand. There is a piece of metal that is still lost in my office/shop - it went to it's hiding place at high speed not long ago. Whew! I may add a Kevlar vest to my safety tools!

Gotta get some shuteye ... JCD