clocking in a mill vise. Problems.

Hi,

I've come back from taking a short break from the workshop. I don't know if i'm going senile here but i can't seem to dial a mill vise in parallel using the dti without throwing it out, normally by 0.1-0.15mm, as tighten up the bolts again.

It's not that i can't find parallel, i can normally get it to the 0.02 over 6 inches of travel no problem. It's literally just as i come to tighten it up.

It doesn't matter if i keep one side pinched up or if i use the lightest of touch on the spanner. Is there something i'm doing wrong here?

Michael W

It sounds as though the base of the vice is not flat, or you have left a pound coin underneath it (ha ha). Or it could be that one of your holding-down bolts is bent, or offset in the slot, so the tightening bears on the side and not the full width of the mill surface.

Or it might be that the table is loose on its mountings, and moves as you pull on the spanner.

All of which I'm sure you have checked. When you have checked the obvious things, only the 'of course it can't be that' things are left...

Cheers, Tim

Thanks tim,

Well it's probably been a while since i last cleaned the mill table so it's due a good clean anyway.

Really i wouldn't be entirely surprised if the base was out, i've got a couple of other vises i can use in the meantime, but it would be worth checking.

It would be worth eliminating those variables anyway.

Come to think of it, i did take a facing cut either side of a piece of ally and found a 0.1 taper on the face. And i know it's not the mill head causing that because i recently dialled in the mill head from using it at an angle on a different occasion. 

Michael W

Edited By Michael-w on 26/08/2018 17:55:20

Two things to try:

1 - a washer under the fixing nuts

2 - a sheet of clean paper between the vice and mill table.

If you can normally get the vice to 0.02, I doubt the vice will have warped or moved since you last used it. What have you done different to before?

Thanks Neil,

I would say the standard washers with these kind of vises do look a bit on the flimsy side anyway, so i could do with making/putting some better ones on it.

Hi Jason,

What i mean by that is that before i've started to clamp it up, the reading is to 0.02mm, but as i start the clamping the reading starts to get worse until i end up at the 0.15mm mark normally.

I admit, It may have been doing this for quite a while if i simply trusted the reading before the nuts clamped down and didn't bother looking twice. 

Edited By Michael-w on 26/08/2018 18:00:57

.

Maybe worth inserting as 1a in Neil's list

If there is discernable draft angle on the top of the vice casting, try milling or spot-facing a horizontal surface for the washers to seat-upon.

... If your washers are 'digging-in' at a point on their edge, there is more tendency for them to act as an unwanted 'drive mechanism'.

MichaelG.

Perhaps the torque on the spanner is moving it? Could perhaps try setting it up with a -0.15 error and tightening, it might bring it to zero.

Brian

Okay,

Had another crack at it today and i think i've solved the problem, there are a number of factors that may or may not have come into play with the error.

-Giving the machine a good clean. Was a minor amount of grease and stains that needed de-greasing, and scrubbing but gave it all a wipe down afterwards and put a thin rub of WD40 afterwards to help ward of the rust monsters.

-Those washers really were flimsy! one had bent right out of shape under repeated duress i assume. So i got some washers that were about twice as thick and replaced both of them.

- I have a bad habit of taking the parallel reading off a big vertex gauge block, clamped up inside the vise, which isn't really proper, but this time i did the right thing and took it from the inside of the fixed jaw.

-The vise is pretty durable, i like this model that much, that i have a second one also. But it comes with a swivel base, which is really not useful 99% of the time. But hey.

I had another habit of clamping the base and adjusting the vise on the radial slot, which in hindsight probably may have contributed to the encouragement to twist away. So i left that clamped up and adjusted the vise along the table clamp tabs this time. One pinched up gently and the other a bit looser.

- My number one culprit that i suspect may be the worst of them all. I noticed as i was doing up the bolts that my spanner would catch the draft angle of the casting. Sounds so stupid looking back but definitely very easy to overlook.

I think you can just about see the radial draft near the base of the index markings. Urgh.

But after all this i was able to repeat my adjustment to 0.02 maximum along the length of the vise and NOT let it go walkabout during tightening.

I'm happy with this as i'm only making an aluminium clamp for a laser sight attachment to an air rifle.

Like many times in this, you start out on one thing only to start sorting out something else first.

Thanks for all the pointers,

Michael W

Michael, I noticed that you are using bolts to hold the vice down. I was told (many moons past) that this is not a good idea. Firstly because if the bolt is too long it will bottom out and jack the tee-nut up possibly damaging the the slot. Secondly because many tee-nuts are not tapped all the way through, basically as if a taper tap was used. This to allow a stud to tighten into the nut and not go all the way through preventing the stud hitting the bottom of the slot. If you tighten a bolt into such a tee-nut it will get very tight and difficult to turn.

I believe the recommended way is to use a tee-nut and stud with a nut and washer to do the clamping. Others will possibly have different ideas!

John

+1 for studs and nuts only to be used to secure vises to machine tools for exactly the reasons mentioned. Do not use bolts, ever, or you'll likely be writing into the forum about fixing broken T slots or holes punched in mill tables ( a LOT harder to fix than to find or make some studs.)

I didn't know that so, i wondered why some t-nuts are not tapped the whole way through!

These bolts in particular are very short, i cut them myself! You can't see it from the photo but they are very dumpy.

But still, i will probably do this in future now i've been told. Especially since at least a stud can't have the head twisted off and saves cutting to length.

I also am not too keen about having a mill with a great gouge in the table. I ought to make some bed way covers as well as i get sick of trying to pull bits of swarf out of them. 

Michael W

Edited By Michael-w on 27/08/2018 17:58:37

I have just written a longish reply and lost it whilst trying to add a photo.

Are there any detailed (for idiots) instuctions on how to do this?

Posting photos

Well 11years of using the supplied bolts, washers and tee nuts that came with my vice and no damage to report

Jason - You are probably one or all of the following:

skilled and experienced at using and not abusing tools

careful

lucky

They only get used for the vice and I know the length so no risk of jacking the tee slot. Studs the rest of the time.

I often use bolts into T- nuts - but with nuts below the bolt heads to effect the actual tightening. It also has the benefit of tightening down with no risk of a stud turning, as the nut is tightened, and possibly pulling at a slightly different angle. So effectively a stud but with a spanner hold on it. Only downside is needing two spanners... so not too much of a hardship.

Duplicate post.

Edited By not done it yet on 27/08/2018 19:26:23

All of my T nuts have had the bottom of the thread staked or peined over so the stud or bolt can't screw in past the bottom of the t nut . I took my vise off the swivel base as it gives i bit more headroom and removes any risk of the vise swivelling when not wanted and lightened the load up on the table .

Merlin , i have done the same thing more times than i care to remember - annoying isn't it ! The thing i find really irritating is the ads on the side of the page as i use an old ipad , the slightest brush against the side of the screen with a finger or thumb seems to open a new page for the ad but when you want something to open i usually have to tap the screen a few times ! Might be time for a new ipad me thinks !