Milling Vice Spec

[Kim GarnettParticipant @kimgarnett94824]

Hi when clamping with a milling machine vice on parallel block how much tilt from the top jaw when clamping is the normal as looking at milling vices this specs is never given. I bought a 5 inch machine vice from J&L some 28 years ago which was made in china I think not sure and to be fair its not been a bad vice for 99% of the time.But using it on a part that I have just made where I had to have surfaces parallel to within 2 thou of each other which at first you think was easy but when i machined i got taper of about a thou in the Y direction over 40mm which is what I would expect as the top jaw pushes the part up this then only leaves me a thou tolerance on getting the height right.There is very little error in the X direction over 3 inches may be a couple of microns.

After making the part I striped the vice put it on the surface table and measured the flatness of the surface which was out over the total length of about 9 inches and the error was about 2 to 3 thou from the hard jaw to the end of the vice. Now is this error correct as when you open the vice you have less contact with the jibs meaning that the top jaw is not as tightly held if they were parallel or is the taper there to tighten the jaw as moving up the taper compensating for the reduced contact area of the jib.

Kim

[Kim GarnettParticipant @kimgarnett94824]

[JasonBModerator @jasonb]

I measured the 3 vices that I have a couple of years ago and got the results below. This is why it is generally

suggested to knock the work down.

[Mike PooleParticipant @mikepoole82104]

The fixed jaw must be square and can be used as a reference, using a round bar between the moving jaw and the work should ensure the work seats firmly against the fixed jaw. Also consider that a vice may flex if it is tightened over enthusiastically and is not of the most massive construction. Zero moving jaw lift is probably impossible but on a high quality vice in good condition it will be small. The design of a Kurt vice does attempt to eliminate jaw lift.

Mike

Edited By Mike Poole on 25/03/2023 10:20:19

[Kim GarnettParticipant @kimgarnett94824]

Hi Thank for the reply This helps if the base is tapered then tapping down with a hammer will not do any good

as the bottom surface is not parallel with the bed .002" per 9 inches so there must be a tilt in the y direction

now is this taper supposed to be in there as the jaw move backward there is less contact with the jibs but with the taper the top jaw tightens as the top jaw is opened? when I measured my first thought was the taper needed to be removed but thinking about I not so sure as the part i have just machined was 96mm long in the Y direction so the vice is nearly fully open which leaves quit a lot of over hang and not much contact on the jibs.

[Kim GarnettParticipant @kimgarnett94824]

Hi Mike thanks for the reply the round bar may help with the jaw lift but i am not certain that the error is all to do with lift as the base to table has an error now is this taper trying to control the lift as the top jaw is opened fully in which case it may be compromise between controlling the lift and small error due to the taper.

Kim

[Clive FosterParticipant @clivefoster55965]

When you get to tenths thou and similar level errors process becomes almost more important than dead-nuts equipment accuracy. So long as your vice or other tooling is decently good the closeness to "perfection" of the job or set-up depends on how you approach things and how well you do the job.

I tend to the view that most of then time your true grip reference is the fixed vice jaw. So long a that is true and vertical a decent set up can be achieved even if the vice base isn't dead flat relative to the mill table or exactly perpendicular to the vice jaw. So long as the component is sturdy enough to grip without distortion something can usually be worked out by appropriate selection and positioning of parallels along with use of resilient packing or a roller for line contact on the moving jaw.

Generally I favour resilient packing, eg soft aluminium, as being easier to handle than a roller.

One day I shall experiment with magnets and a D shape packing piece set flat side to the job to combine the flexibility of a roller with a larger contact area on the workpiece..

My normal use vices have a very slight perpendicularity error between the fixed jaw and the base. Just enough that if 1/4" wide parallels are placed next to the fixed and moving jaws with a robust test piece having truly parallel sides around 2" or more wide gripped between the jaws and beaten down the parallel next to the moving jaw is just loose enough to slide out with moderate pressure. Depending on the job I either rely on the parallel next to the fixed jaw to set position, but still fit one close to the moving jaw to ensure things don't tilt objectionably when beating down, or put two parallel at the 1/3d jaw separation points. Seems to work adequately as parts look too be standing up straight.

Clive

[Kim GarnettParticipant @kimgarnett94824]

Hi Clive I can't agree more as stated earlier the vice is 28 years old and it was not expensive when I bought it and I have used it quite lot and done some decent stuff with it and had not many problems with at all. However this last project has been a right pain I did managed to a finish the parts but it was not easy with very little room for error due to the taper I did find some information on a machine vice they were stating 0.02 in 100mm which slightly better than what I have got . Jason information was very useful as it shows that the vice in the y direction can be better. so today I have stoned the working area of the vice base parallel in both x and y axis so these are parallel with the table which was tested with a 123 block sitting the base with jaws open and the block laying flat error was less than 0.01mm in x and y axis checking 3 inch long edge in both directions which gave a big improvement on what I had before in the Y axis no change in the X axis then checked It with the vice closed and the block tapped down and got almost the same result . I have been lucky as where the top jaw runs on the edge of this surface it was slight lower than middle part see photo which means I have not touched the area where the top jaw runs so if the taper is required to restrain the lift in the top jaw I have not touched it .

[Martin ConnellyParticipant @martinconnelly55370]

I think the only thing I ever really checked on my 6" Eclipse vice was the fixed jaw's perpendicularity. That is easy to get right with a bit of shimming and/or stoning between the vice body and the jaw. Then, as suggested above by Mike, that is your reference surface for all future work. When I put a 123 block on parallels and pinched it with a roller between the 123 block and the moving jaw both parallels had the same feel of resistance to sliding out so I didn't go further than that. Across the vice bed has always been fine based on the results of surfacing both sides of a workpiece. It could be argued that if you have a well set up fixed jaw then for a lot of jobs one parallel is all that you should use, the second parallel just helps with positioning the part in the vice before it is tightened (a third parallel helps position a roller in this situation).

Don't overtighten the vice either, this will always move the fixed jaw relative to the base as nothing is perfectly rigid except in mathematics.

Martin C

[SillyOldDufferModerator @sillyoldduffer]

Posted by Kim Garnett on 25/03/2023 20:41:53:

… I have not touched the area where the top jaw runs so if the taper is required to restrain the lift in the top jaw I have not touched it .

Hope I've understood this one!

As far as I know putting a deliberate slope on the base of a vice isn't a way of restraining lift. More likely, I think, an inexpensive vice was accidentally machined with the slide and base not quite parallel. The slope causes a small problem when the jaws are close together, but worse when they're far apart.

So I think correcting the problem by stoning as Kim describes is the right answer. (If de-sloping required a lot of metal to be removed, I'd mill the vice.)

Stuff lifting in the jaws when they're tightened is another issue, very common, but tapping down with a hammer works for me.

Dave

[Kim GarnettParticipant @kimgarnett94824]

Hi All the question was is the taper on the base there for a reason limiting the top jaw lift as the vice is opened outward or is it just poor quality in manufacture ?.

Kim

[Clive Brown 1Participant @clivebrown1]

Can't see the taper as deliberate to compensate for jaw lift. Would that really work? 2 -3 thou in 9" seems as much as I might expect for a low-cost Chinese vice made 3 decades ago.

[Kim GarnettParticipant @kimgarnett94824]

Hi all that was my first thought , but I have a second vice which is 10 years newer which I purchased when I bought my bigger mill. I don't use this much as I do most of my vice work on the smaller mill with the above vice. Now if you had asked me which vice I preferred using I would have said the early one as it feels tighter. Today I have checked the newer one that I own which is the same vice and it is parallel not sure that it came like that as a toolmaker I use to work with checked it out and has reground most of the surfaces when I got it. That said when the vice is opened towards it limit it feels loose in comparison to the early vice. This is where I thought is the taper there on purpose and the fact it is in one plane and near perfect in the other.

Kim

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