Installation techniques for a benchtop lathe

[Wheels17]

I'm a bit confused by some of the advice that I see on various forums about setting up a (benchtop) lathe. People seem to spend an inordinate amount of time and effort with expensive, high precision levels and shims. It seems to me that what they're trying to do is get the critical parts of the lathe in one plane, rather than truly level. Then they bolt the lathe to a heavy wooden top, that's going to move all over the place with temperature and humidity.

Most wood has low thermal expansion(2.7-3.0x10-6 in/in oF) but dimensional changes with moisture are very large. From 20% RH (winter) to 60% RH (summer), the moisture content ranges from 4.5% to 11%, with an expansion of 6%, with varying changes in the length, width, and thickness. Wouldn't this destroy all the careful work installing the lathe? Finishes on the wood would slow down the movement, but the movement would still occur. Steel has a bit more thermal expansion(7.3x10-6 in/in oF) than cast iron (6.0x10-6 in/in oF), but has no humidity effects and my shop is pretty well controlled for temperature.

I've seen 1 1/2" MDF benchtops, which would have much more uniform properties, but they still move about 2 1/2% over the same humidity range.
(Data at http://www.pbmdf.com/cpa30/files/ccLibr ... bility.pdf)

If you really wanted to isolate the lathe, it seems like it should be on a 3 point support. Or is there some sort of a middle ground? I have a crowded shop and really need to move the tools around as I work on different projects. I've been considering a square tube or wide c channel sub-base with 3 point support on a rolling cart.

I'd be interested in hearing what people with more experience would suggest. (this category probably includes everybody on this board)

[wsippola]

You're correct of course that a wooden bench will move, which makes levelling it somewhat futile. I suspect a lot of benchtop lathes are nowhere near level, and depending on their design and size, it may not be any real problem.

You don't need a precision level, you can center the tailstock and then tweek the mount to get the best results, which is the primary reason for levelling. Hard to do if the tailstock ways are worn. Search for "Rollies Dad's" method if you want details.

Wayne

[samthedog]

How much precision do you need? Considering that it is a bench top lathe I would think that rigidity would be a bigger concern when looking at accuracy than thermal expansion of the wood. If you want to increased rigidity compared to that of wood and decrease the thermal expansion, why not pour a concrete slab and mount that on a steel frame. If the air is a consistent temperature over the shop, you should have very little variation in the expansion rates of all the legs and therefore even if the legs expand or contract, they will do this uniformly. The concrete will add mass once the lathe is bolted down and this will reduce vibration. Just a thought...

Paul.

[hammermill]

adding a concrete bench top will deffiently improve thing on a small lathe. the mass alone dampen lots of vibration and add stability.
consider the main purpose of leveling is to get everything in a consistant plane. otherwise shipboard work would be inpossible, would it not?

[Falcon67]

I don't have any special precision issues using this $399 lathe mount:


I modify transmission fittings for race transmissions and can easy hold +/- .001. The head stock is bolted fairly snug and the tail end is just snug. Use bolts, washers and nylock nuts to keep things in place. Easy to move around and everything machine related is in the cabinet. If I got real concerned about the wood top moving around, I'd sheet the lathe end with 1/4" steel plate.

[stevec]

Show off!

[John Hill]

My 12x36 lathe before fixing down to my concrete bench.


IMGP9332 by aardvark_akubra, on Flickr

[Falcon67]

Show off!

[JohnAspinall]

If you really wanted to isolate the lathe, it seems like it should be on a 3 point support. Or is there some sort of a middle ground? I have a crowded shop and really need to move the tools around as I work on different projects. I've been considering a square tube or wide c channel sub-base with 3 point support on a rolling cart.

I'd be interested in hearing what people with more experience would suggest. (this category probably includes everybody on this board)

I certainly don't claim much experience, but for what it's worth, I went the C-channel route, and (so far) have no complaints.
Pic here: http://www.chaski.org/homemachinist/vie ... 26#p178126

[SteveHGraham]

It can be very hard determining whether the people giving you advice are painstaking craftsmen or just anal-retentive. This has been a big challenge for me. Don't get too caught up in setting the lathe up perfectly, until you see what it can do.