Pros and cons of square vs vee/dovetail ways?

I'm curious as to the advantages and disadvantages of various slideway geometries. In particular, what would possess a manufacturer to use square ways over vee/dovetail ways and vise versa? Anyone got any wisdom on this?

Dunno. Van Norman used both on their milling machines, post World War One. Generally the larger machines used the square ways, so you might conclude some benefit to production in larger sizes. They even made some machines where the saddle Y-axis was dovetail on one side and square on the other! I am uncertain if these mixed-ways machines were all of a particular model, or just a time span of a particular model, as the photos I've been looking at are not always accurately labeled (thank you, eBay sellers, not very much).

just my opinion so don't beat me up:
I think the V ways were designed with soft ways and so allowed the opportunity to maintain a machine back to new with scraping.
As the heat-treat ways came to be it was learned that the way might outlast the rest of the machine.

after a few major builders came out with square way it became more accepted that now the square ways are proved ok/good and for some reasons better.

Square way machines can be produced on a boring mill or a planer. Dovetail ways are produced only on a planer.

Every heavy machine I have seen use sqr ways, Bullard, G&L, King, K&T , Cinn. and others, I have never seen anything but v and dovtails on light machines and lathes...Phil

The flat ways on heavy mills is for heavy loads. there is more square inches of contact on the ways.
As always, one cant gain in one area, without losing in another. The flat ways are subject to a small amount of yaw because of the clearance needed for oil film, and smooth operation, so, being aware of the error one can avoid it.
V ways in good condition prevent the carriage from twisting or yaw.
The American Pacemaker uses 2 V ways for the carriage, claiming more equal wear in time compared to a V and a flat way many lathes use for the carriage.
The worst example of excessive carriage twist or yaw can found on Atlas lathes, but starting the tool an inch ahead of the work piece allows most of the twist or yaw to happen before the tool inters the work.
Hardinge dove tail beds the same thing, there is no getting around giving the carriage a couple of thou clearance so it will move on a new machine, again starting the carriage an inch a head of the work piece will give more consistent results, more so on worn machines.

Just rambling ...

Surface area ...

Independent adjustment, this-away and that-away ...

Consider the angles and clearances for oil. A square way with a thou' clearance can only lift a thou'. A 60° dovetail almost 2.

Load a Bridgeport table off the side of the knee. Gets sticky to move the saddle. Not a lot of area to take the load on the opposite side dovetail. I'd guess my Lagun has at least twice the area taking that load at 90° instead of 30.

V ways tend to be self aligning as the way surface wears. The carriage remains constrained in the horizontal and vertical planes. It slowly drops downs as the wear progresses but remains in contact with the lower guides.

Box ways do not have this advantage. They require the use of gibs to compensate for wear.

In practice, with either design, a machine will be taken out of service when the ways become worn in mid span.

One advantage of the box way design is that there is no tendency for the carriage to climb up the V way when there is a large side load.
Lathes are equipped with a additional guide surface with adjustable gib below the V way to prevent carriage lift.

Another advantage is that additional vertical load bearing surface area can be added to a design without changing the height of the way. With a V way adding more horizontal surface also requires a corresponding increase in height. This will not be a optimal design if one of the goals is to minimize total way surface area to reduce carriage friction.

Manufacturing is another consideration. It is more time consuming to fit a double V way carriage than a box way carriage.

The advantages of no way climbing, reduced friction, and ease of manufacture and rebuild are significant for larger machine tools.


There are other considerations when hydrostatic rather than squeeze film lubricated ways are used. Hydrostatic V way designs will not jam if there is machine frame twisting from thermal gradients. The carriage instead will move to a new equilibrium position.

A box way machine will jam due to the small clearances between the carriage and guide rails. It is very difficult to keep the box way and carriage straight and parallel within .0005 inches along the length of a machine bed measured in feet even with coolant circulating through the bed and carriage.

There are two approaches to eliminate the problem. One method is to use a short length carriage., The length is chosen to insure that under the worst case thermal gradients the clearance gap will not close. Hydrostatic diamond turning lathes use this design.

On the long carriages used on cylindrical grinders the solution is to have either floating gibs, pads, or pistons supplying the pressurized oil along the length of the carriage. The pistons maintain a constant clearance to the box ways by regulating the oil flow rate. These machines are significantly more expensive to construct compared to a V way design, The expense can be justified when the close tolerance parts produced on these machines eliminates the need for selective assembly.

Just a Sparky said:

I'm curious as to the advantages and disadvantages of various slideway geometries. In particular, what would possess a manufacturer to use square ways over vee/dovetail ways and vise versa? Anyone got any wisdom on this?

Click to expand...

Some of it has to do with the geometry of wear and how much the positioning is affected BY wear, hence "longevity" in service before major maintenance is required.

An inverted Vee way OR a dovetail, the shape affects or controls TWO axes in one shape, related. Wear affects both, and often unequally, yet they wear with "gravity" as an automatic adjustment.

Rectangular ways may otherwise need more frequent attention to gib adjustment .... unless significantly over-built. Or less destructively USED.

Read: A(ny) HBM, or even a light-lathe's turret tailstock slide - can last a long while.

An inexpensive "Lathe Shaped Object" with rectangular ways, OTOH, isn't even good enough to joke about!

A rectangular way, each axis has a high degree of independence (theoretically 100% separate), one from the other. The vertical mass load may be significantly higher than the load imposed to meet the "positioning" challenge.

Wear - and repair of it - may largely fall on one surface, only minimally affect the other. Or not.

MANY machine-tools, rectangular ways do not see a lot of active TRAVERSE whilst in the cut. Whatever they serve may be positioned and LEFT there whilst other parts move to do the work.

They "usually" have the advantage of actually being "Tee" shapes. This can make clamping easier and simpler in less space.

Vee ways are more often found where there is constant traverse, not just set up positioning. Clamping requires a separate, but co-axial, surface. Costs go up.

Dovetails are the common compromise, many milling machines, for example.

"Hybrid" shapes exist, too.

A few of the "Grand Old" lathes are noteworthy for utilizing sloped or assymmetrical modified Vee ways that bias the bearing area toward the side that bears the greatest loads. Works well. Literally "lasts a long time".

Even so. it may need a LARGER way ... and more space, overall ... to manage the loads well.

TANSTAAFL They all have their place.

Phil in Montana said:

Every heavy machine I have seen use sqr ways, Bullard, G&L, King, K&T , Cinn. and others, I have never seen anything but v and dovtails on light machines and lathes...Phil

Click to expand...

Obviously you have never seen a DeVlieg.