adding a longer bed

[balsaman]

Anyone ever added the conversion bed to a minilathe, instead of replacing the bed. For example making the 7x10 to a 7x22... by using the 12" bed extention kit bolted somehow to the end of the lathe.

http://www.littlemachineshop.com/pro...ProductID=1525

I am thinking of trying this. If it's impossible, I would like to know before hand...

Eric

[pminmo]

http://www.broncosaurus.net/7x20.html

[CNCadmin]

Good question, I two would like to stretch my lathe.

[balsaman]

Thanks! Just what I was looking for.

Eric

[DDM]

It's doable but it's going to take some time. You might have to do some milling to the extension to make it fit though. Make sure that you've got spaces you can put shims in and that you have a long sturdy flat surface to mount the lathe and the extension to. After you get everything half tight you'll have to figure out a way of running a dial indicator over the joint to the extension and adjust from there. If the bedways arn't flame hardened you could have some fudge work with block sanding. Having a straight good bed on a lathe is a nice thing to have. One of the Lathes at my work has about .003 taper in 3 inches right near the head stock, belive me you don't want that. Just my two cents.

Carl

[Broncobill]

While it takes some work, it's definately possible to extend the 7" minilathes this way. I know of several other who have also extended their lathes this way with good results. The concept is pretty straighforward & as always the devil is in the details. I think the most common stumbling block is the variation between beds where the gibs ride. There are a couple ways around that, one would be to mill or file a uniform surface on one bed to match the other. I chose to go the adjustable gib route, it's a less perfect solution but it had the advantage of being simple. I simply adjust the gib to allow it to ride best over both halves. It's not like I'm doing fine pitch threading that far from the headstock.

a few folks have gone with a much shorter extension ( in the 4"-6" range ) and have gotten good results. That had actually been my original idea, to just add a small extension where I could "park" the tailstock and gain some usable real-estate. Once I started playing around with it I decided to add some significant length and the website details what followed. The same idea would still apply though, take one of the LMS extended beds, combine it with the setback tailstock and then add a small extension to park the tailstock on and you'd have something in the ballpark of a 7x17. The bed kit & tailstock alone get you to a 7x15 & extensions only add to that.

Dave
www.broncosaurus.net

[balsaman]

what do you mean "variation between beds"? In what way do the gibs vary?

Thanks,

Eric

[Broncobill]

The gibs themselves don't really vary any more than the rest of the machine does. What I meant was that the gibs ride along the bottom edge of the bed, and while this is a machined surface there doesn't seem to be a whole lot of QC involved when it comes down the the actual thickness of each & every set of ways. The most common problem that crops up when doing this is that the ways of the donor bed are from a different batch of castings and the ways are marginally thicker or thinner than the bed of the original lathe. If you're lucky the two beds will be very close in size and it's not an issue, otherwise there's going to be a step at the joint and the gib will catch on it. If the step isn't too bad you can run the gibs a little loose but that compromises accuracy and only gets you so far anyways. The best solution is to make the two even by either milling down or building up the outside edge of the bottom of the ways where the gibs ride. For some reason most of those I've talked to had donor beds that were thicker so it was a matter of milling or shaping the edge down a bit to match the original lathe. The only one I know of that had to build the area up did so with moglice and seemed happy enough with the results.

Dave
www.broncosaurus.net

[Bloy2004]

If one does this extension by obtaining a "replacement" bed, then by taking the smaller of the two(if they differ from casting lots), and using that as the main machine bed, then the extension bed would only need to be taken down instead of being built up to get the two sections to align.

..just my $.02 worth..

[balsaman]

Are we talking the flat (rear) section of the ways, or the front half hex shaped part, or both. I can see machining a few thou of the flat section if need be...

Eric

[ballendo]

Eric,

There's a yahoo group devoted to this, called 7x25 cnc minilathe, or some such...

Pictures, examples, discussion.

Hope this helps,

Ballendo

[balsaman]

found it, thanks.

Eric