Turning plastic on a metal lathe

I've never used a lathe, but have been reading up on them a bit. My overall shop skills are mediocre compared to you guys. I want to precisely turn plastic. I want to turn with precision, and there's stuff for which I'll need a vacuum chuck.

First, I don't need to turn things with an accuracy of 0.001 mm, so in some respects a metal lathe would be overkill. However, I will need some precision. Considering a Grizzly 7x12 is made for precisely machining small parts, I'm thinking that this might be the way to go. Also, since metal lathes have tool holders, I'd guess that it's better to use one instead of a wood lathe.

It's my understanding that vacuum chucks aren't made for metal lathes, only for wood lathes. Is it possible to use one with a metal lathe, or are they built too differently? I'd be using VERY low RPM, so there is no chance that the piece would fly off and be dangerous.

It seems to me, that vacuum chucks are a long metal tube for a spindle, attached to a vacuum chuck at the "cutting end", and extend out the "back" of the lathe. I don't know how air is attached to the spindle. I'm guessing it's not attached DIRECTLY to it, but maybe to something that's around it. I don't know how the spindle is turned, either. I'm guessing there's a belt, etc. within the lathe that makes contact with it. Can you fill me in on this?

How well do the vacuum chuck spindles hold true to center?

I wouldn't be working with anything over about 1.5" in diameter for plastic. I might have need of some metal parts too, and I don't know how long they'd need to be. I'm considering the grizzly mini lathe, 7x12. Would this be a good choice? I've heard that these lathes take a little bit of tuning in order to work. Is the tuning something I could do easily, or should I hire someone? I don't have a milling machine.

For basic work, what sort of accessory items am I looking at? I'm guessing I'll need at least three different gauges. Are these items that I can go cheaply on, since I'm not looking for extreme precision? I'm hoping to put as little money into this as possible.

I'm sure I'm overlooking something. If anyone can offer some advice, I'd appreciate it.

I suggest don't buy a grizzly anything. One problem with these types of lathes is once you got it you got it. You can't sell it without taking a big loss, you can't much extra for it, and down the road forget parts.

I like the idea of finding an older belt drive lathe of some sort- South Bend for example, that you can put 5c collets in (very good for small parts), a 3 jaw chuck, and a 4 jaw. Even if the lathe does not have all this stuff you can find it. I say belt drive because I think if you get wrapped up in it you are talking probably broken bones not dead (probably).

Then look on line for the book "how to run a lathe". This is good basic starting info.

Precision turning of plastic? Maybe plus or minus .002 inches....... Not PVC or Nylon.

kid5084 said:

Precision turning of plastic? Maybe plus or minus .002 inches....... Not PVC or Nylon.

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Oh c'mon. Unless it's a really thinwall shape you can hold a thousandth pretty easy.

I make a bushing on a regular basis that has a +/- .0005" bore in Nylon MD. They come off the lathe fine, and they are on size when I deliver them.

I tell the customer not to expect them to stay that way, but they have never complained about them going out over time.

I have samples set aside from different runs so I can watch them and get a sense of how much they move. I have one part from last February that was .250/.251 on the bore. The .250 gage pin goes and .251 does not go, but the part is growing and the .251 pin is starting to go. So maybe it's moved a couple tenths in 6 months.

I have 6 parts of a different dash number from June that were .253/.254 bore, and they have not moved over the two months since I made them.

Vacuum can grip flat parts, but the strength of the grip is limited by the area of the part and by the quality of the device that provides the vacuum. Small parts and inexpensive vacuum chuck and pump and inexpensive lathe adds up to wasted money.

A perfect vacuum is about -14.7 PSI. There are no perfect pumps, so you will get a lower number, depending on whether you have a $500 pump or a shop vac. The $500 pump can provide around -13 PSI if there are no leaks. That means no more than 13 pounds of suck on a 1 square inch area and much, much less with a shop vac. It would not take much of a lathe cut to overcome that sort of gripping power.

I have a Ryobi vacuum table that uses a shop vac to provide suction. It works fine to hold a 3 foot x 3 foot piece of plywood while I sand it. It is useless for small parts.

You might want to look into using double-sided tape.

Larry

Pete Deal said:

I suggest don't buy a grizzly anything. One problem with these types of lathes is once you got it you got it. You can't sell it without taking a big loss, you can't much extra for it, and down the road forget parts.

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I hear you I got the McGrizzled 12x24. I passed over the mini lathes to get something that could power feed in both directions and forward/reverse. I put a DRO Pros brand DRO on it. I can hold a couple/few tenths making simple pins and the like. It does ok with AL, pretty sad with anything tougher than that.

the more I think about it, the more I think I might be able to get away with not having a vacuum chuck. So, it was mentioned that a belt-driven lathe would result in broken bones. How is this better than a gear-driven lathe?

I saw this lathe used:
Craftsman Model # 19263 6" swing mini bench lathe jeweler machinists tool

The difference between it and the Grizzly, aside from the obvious superior craftsmanship of the vintage Craftsman, is that it seems like precision adjustments can be made to the carriage of the Grizzly with micrometer wheels. It seems, and I could be wrong, that the way to adjust the Craftsman is to loosen a knob holding the carriage in position, put the carriage into position relative to a micrometer (or whatever) measurement, and then tighten it down. Maybe I'm mistaken. Maybe the knobs I'm seeing aren't for tightening/loosening a position, but are actually non-locking controls for worm gears. If it's the case that I have to manually set a position and then tighten it, I can't imagine being able to accurately hold the position as I'm tightening it in place. This has been my big reluctance to get something like this. I have no idea where I'd get belts, either. I'd like to get something used, though. Decent resale would be desirable.

By the way, it seems that there's no way that the center of the chuck and the center of the "live center" would be aligned out of the box. I'm guessing some sanding would have to be done to get things aligned, right?

I'll check out that book. Thanks.

You may be better off to try at the link below. Folks here just do not use the machines you are talking about, and cannot give useful information on them. At the link, there are many professionals and ex-professionals who can give good info, and may actually own machines such as you mention in their personal shops.

The Home Shop Machinist & Machinist's Workshop Magazine's BBS

Im in a similar position as you just starting out. I got a deal on a jet 9x20 and have spun a little bit of Delrin for making bushings and it worked fine. I can’t imagine needing a vacuum chuck for anything under 1.5” though. My neighbor had one on a wood lathe for turning big birch bowls and it was pretty cool. He rigged it up with a cheap Venturi vacuum pump that ran on his compressor


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If you don’t need a threading the Hardinge DV 59 is a hell of a deal used if you need a tailstock.
Or if you need power feed the HC.

Like all materials feed/speed/cutter geometry control the finished part...onless your machine is crap to start with.

That Hardinge, though nice looking, also looks massive. Thanks for the link, I'll check 'em out.

I know I will probably get flayed alive for this, however...
I have used cyanoacrilate glue to mount small parts for lathe work. Just apply gentle heat to release. Be aware acrilate glues will fog some types of plastics. Also plain tap water makes good coolant.
Most important stay out of the firing line when glue is primary means of fixation.

doug8cat said:

Also plain tap water makes good coolant.

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Beg to differ. Most plastics cut best dry.

Also, most plastics are hygroscopic. Size is strongly affected by water content. If you are going to make anything that will be submerged, let's say bushings for an r/c boat or pump rotors, then put the blanks in a bowl of water for a few days before you machine them.

Pete Deal said:

I suggest don't buy a grizzly anything. One problem with these types of lathes is once you got it you got it. You can't sell it without taking a big loss, you can't much extra for it, and down the road forget parts.

I like the idea of finding an older belt drive lathe of some sort- South Bend for example, that you can put 5c collets in (very good for small parts), a 3 jaw chuck, and a 4 jaw. Even if the lathe does not have all this stuff you can find it. I say belt drive because I think if you get wrapped up in it you are talking probably broken bones not dead (probably).

Then look on line for the book "how to run a lathe". This is good basic starting info.

Click to expand...

I disagree , in the shop I have worked at for 28 years we have a large new Grizzly lathe that works just as good and holds tolerance just as well as the LEBLOND lathe sitting across from it. and another thing we have just bought a Grizzly horizontal 10 inch band saw that is by far the best saw Ive ever used , the hydraulic feed control is fricken awesome . I know that speaking of the evil Chinese products are a tabo here , but not everything they make is total crap . and for anyone saying I don't know what I'm talking about , these machines are used in a very large industrial MFG company , not some hobby machinist shed . I get so tired of every one talking shit on the machines I run daily .

Did the Grizzly work well out of the box, or did you need to machine things to fit properly?

Mine was fine. Not the best quality machine, but it paid for itself quick enough. Note, the tooling that may come with it will be garbage. Throw it away immediately and buy some quality stuff. I just get the dovetail toolholders from them as they are non standard. I'd avoid any "mini" machines, the likes of little machine shop. I got a mini mill from them which was fine as a drill press, but pretty much a POS otherwise. There was one lathe they had that did power cross feed, but only one direction. Reminds me of the remote control cars that could only turn right by backing up to the left! It's a tough call: buy used better quality machine when quality on a used machine can be hit or miss or buy import "crap" new. To me, the import machines are like a drug habit. I'm not proud of it. I did it because I had a budget. I might do it again Seriously, I'll be looking to get a drill press/ face stock machine at some point and I'll be curious if the forum can talk me out of the G0755.. but another day. I should keep my import chat to a minimum over here.

Just to let the OP know that thin disks and shapes can be done with a vacuum plate on a small lathe. Longer parts NO! The attached photo shows a 102mm, 62, and 52mm plates that we used on .24 thick plastic to face and bore a through hole. Did thousands of these squares, they were milled to a precise dimension and the "fence" around the outside drove then. Deublin rotary got the vacuum to the rotating spindle and tubing with oring fittings transmitted the vacuum to the fixture mount, swapped the individual chucks on the one mount. It was an involved set up and all the ducks were in a row.

jumpinjimmy447 said:

I disagree , in the shop I have worked at for 28 years we have a large new Grizzly lathe that works just as good and holds tolerance just as well as the LEBLOND lathe sitting across from it.

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Ya maybe if the LeBlond was completely clapped out, but even then i doubt it.

FredC said:

Just to let the OP know that thin disks and shapes can be done with a vacuum plate on a small lathe. Longer parts NO! The attached photo shows a 102mm, 62, and 52mm plates that we used on .24 thick plastic to face and bore a through hole. Did thousands of these squares, they were milled to a precise dimension and the "fence" around the outside drove then. Deublin rotary got the vacuum to the rotating spindle and tubing with oring fittings transmitted the vacuum to the fixture mount, swapped the individual chucks on the one mount. It was an involved set up and all the ducks were in a row.View attachment 235255View attachment 235256

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That looks like a few thousand bucks worth of tooling as well. It would be an insult to put that sort of thing on a Grizzly machine;-)