Knee or Head

[Bruno TaylorParticipant @brunotaylor21701]

Hi David

I had the same internal debate before deciding on the VMC. Basically it came down to the fact that a moving knee is the same configuration as larger industrial mills so good provenance. In use it operates like a real mill, whatever that is, and with 3 axis DRO, which is esential in my opinion very easy to use. I am extremely pleased with mine.

A drawback l have heard of WM18 and their like is that you are forever reaching up high to the vertical movement wheel. Even on the VMC its a bit of a reach to get to the drawbar, and l am 6ft+.

I know there are similar from other supplliers but paying for delivery/install from Warco was well worth it. The mills are suprisingly large once in a small space. Another feature l thought was optional, but has proved essential is longitudinal powerfeed.

An expensive purchase and l am not sure that "she who must be obey,ed' has forgiven me yet.

By the way my mill is the latest with variable speed. Again another reason not to be accessing the top of the mill quite so often.

Best wishes in your deliberations.

Edited By Bruno Taylor on 28/01/2018 19:03:36

[Mike PooleParticipant @mikepoole82104]

I have a Warco VMC and have no complaints. The WM18 has a slightly larger working envelope if this is important for your use. A popular VMC mod is to fit a column spacer to give a bit more headroom but I have not had a problem yet with the standard machine. My preference was for R8 spindle which I would definitely choose again, I do not feel that a morse spindle on a Mill is correct even though Tom Senior went this way. I prefer a knee adjustment for the Z axis as the weight of the knee is an effective backlash eliminator. A DRO may give confidence as to the true Z position with a knee or head machine. Winding the knee a long way can be a minor workout but power feed is an option.

Mike

[VicParticipant @vic]

The VMC is in no way a large machine. I had an Omnimill which was bigger and that was regarded as a relatively small mill in its day.

I’m shorter than you Bruno and I have no difficulty reaching the draw bar so you must have short arms.

I wouldn’t bother with a DRO on the “Z”, the dials are accurate enough for depth of cut.

What is handy though is a scale on the quill for drilling.

Delivery of my VMC went like a dream, Dave, the delivery driver was brilliant and wheeled it straight down my drive into the (garage) workshop and against the wall. Moving house was a bit more tricky but I easily split the mill into three bits for transportation. Reassembly was easy enough.

Most early mills were morse taper, not just Tom Senior. All the machines I looked at about twenty years ago were morse taper except a Bridgeport. It’s still used on some small mills.

[MWParticipant @mw27036]

Posted by David George 1 on 28/01/2018 14:47:06:

I believe that the Z axis on that model is a rack and pinion which has a distinct backlash problem

David

I have the WM16 and I believe the Z axis does have a lead screw, not a rack and pinion, this is just a smaller brother of the WM18, I think it just uses (a pair of) bevel gears to change the axis of the handle motion 90 degrees to the lead screw rotation. .

If you look at some variations on the WM14 you can see the older model where the handle was on top of the machine to drive the leadscrew.

I suppose once they scaled up this smaller model, they realized once ontop of a bench that reaching the handle became more of a problem the bigger they made it. 

Michael W 

Edited By Michael-w on 28/01/2018 19:50:17

[JonParticipant @jon]

Both will have the same problems which ever way you look at it.

Lowering a heavy head on to a job is ludicrous, lock it down and use quill.
Likewise knee type carry a lot of weight hanging off the dovetails, dont expect to be true if not locked up.

[David CanhamParticipant @davidcanham77137]

Interesting comment re locking up both before machining. Just a novice making comment here but I am sure I have read somewhere that extending the quill is possibly more likely to encounter any run out / slack than using the knee to make a cut.

Would it be possible to check the accuracy of the knee with the locks off and then with locks on?

David.

[MWParticipant @mw27036]

Posted by David Canham on 28/01/2018 20:47:51:

Interesting comment re locking up both before machining. Just a novice making comment here but I am sure I have read somewhere that extending the quill is possibly more likely to encounter any run out / slack than using the knee to make a cut.

Would it be possible to check the accuracy of the knee with the locks off and then with locks on?

David.

I've not got a knee mill but I believe the practice is to lock it up for the best results still. Having anything that can move with a bit of slack regardless of how you do it, is still causing problems under the right conditions.

That said, once a milling head becomes so heavy, as they often did on industrial mills with gear boxes and what have you, the only sensible solution was to fix the head and move the table or quill.

Having everything locked up tends to be the recommended practice but then again we can get away with not on things that either don't require a great deal of accuracy or are not putting a great load on the tool.

Michael W

[JonParticipant @jon]

Posted by David Canham on 28/01/2018 20:47:51:

Interesting comment re locking up both before machining. Just a novice making comment here but I am sure I have read somewhere that extending the quill is possibly more likely to encounter any run out / slack than using the knee to make a cut.

Would it be possible to check the accuracy of the knee with the locks off and then with locks on?

David.

Of course you can check accuracy with gibs nipped up and undone.
Mines only chinese so wears rapidly, if i were to adjust gibs it will lock up at ends of travel. Mid ish nip head up and visually see head tilt right to left, nip 2nd lock and head pulls in at top. Opposite happens with knee.

Maybe fine for a well adjusted mill of either type, microns of play can mean serious runout over length.
If you look at Bridgeports and the like they have a nice means of quill drilling and fine milling. Further to that powered quills are made by some.
My quills had it years ago, worn oval through use, even taking the most of the play out with grub screws on to delrin bushes still has 0.38mm movement front to back. Head moves around 6mm from loose to gibs locked up, standard around 1mm.

[David CanhamParticipant @davidcanham77137]

Thanks for that Jon. Keep everything nipped up when machining sounds like good advice to me. No matter how new the machine is and mine will certainly be Chinese.

David.

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