I have never known this happen except when I forgot to tighten the nuts holding it down. I don't think the weight is relevant.

• Are the nuts tight enough?
• Is the base of the vice flat, or are there any burrs preventing close contact with the table surface (on the vice or the table)? Check with surface plate – use blue and or check for any rocking of the vice.
• Are you being too ambitious with your cuts?
• Can you move the vice if you tap the work hard with a hammer or is it just when milling?

If all else fails you could try the trick of a sheet of thick brown paper between the vice and table.

You say bolts rather than studdiing? Are the bolts passing through the T-Nuts or bottoming on the nuts, preventing the t-nuts from being pulled tight. Always use studding, not bolts, because a bolt can break the table by jacking the slot.

Apart from the T-nuts not being pulled tight properly, are they too small, ie, not bearing fully across the top of the slot.

Dave

Edited By SillyOldDuffer on 06/08/2021 10:31:09

As mentioned

The nuts might be tight but are the right surfaces being pulled together

If the mill is not complaining (noisy) when this happens I think I would go for hold down problems, but as somebody said previously are your cuts too ambitious and are the cutters sharp. Plus one for the paper but not thick.

Tee nuts are not tapped fully all the way through. Use a taper tap and only allow the tap to cut a partial depth thread at the bottom, check that a stud tightens before passing out of the bottom. This will prevent you from jacking the tee nut up and locking it into the underside of the tee slot.

Hi Me, the T nuts touching the bottom of the vice would be the first thing I'd have looked at, it doesn't hurt for them to be 1mm or so below the table surface to insure they are gripping under the T slot flange.

Regards Nick.

Since you made the tee nuts yourself did you check they were below the table surface when pulled up against the upper surface (inside) of the slots? They may be below the table surface when resting on the bottom of the slots but that is not what needs checking.

Martin C

Or tap all the way through because it's easier and then upset the bottom of the thread with a centre-punch. Good opportunity for hammering.

Same reason as Howard explains – to prevent the stud screwing all the way through the T-nut and jacking accidentally.

Dave

I have a Warco WM14 and the slots take the head of a 10mm bolt very nicely. I just slide the bolt in upside down and use the nuts and washer on the top of both vice and angle plate.

Seems to work very well. I do have a lot of home made tee nuts.

While noting that RB is a bit late to the party (see first reply), I often use a bolt – but only where appropriate or needs must. Sometimes with sufficient washers to ensure compliance, sometimes screwed in firmly (then backed off by a couple or three threads) then using TWO spanners (or spanner and allen key) to tighten the nut for clamping purposes.

Using only studs should avoid beginners breaking out T-slots.

All my home-made T-nuts are staked, to prevent any bolt or stud threading through. I like the idea of only tapping at full depth part way though the nut, but a better method might be to make a completely blind thread with a ground off plug tap?

Bought-in T-nuts are (generally) better than those made in the workshop because they are hardened (case- or through-hardened?), but cheaper ones are not always sized optimally – deep threads are wanted, but also sufficient swarf clearance below the nut and with flanks as wide as the machine slots permit. Old mart is right about making your own – and paricularly about the length of some of them. I bought in a holding-down kit from Chronos originally but have made quite a lot of extras (both mills have the same width slot but different depths).

I like to see both ends of the T-nut under the item being secured, or under it and any out-board posts – that way it should be virtually impossible to break out a T-slot, however poor the table might be (as long as it is flat, of course).

I sometimes have as many as 14 T-nuts in use on my Centec – not all in use (they cannot be removed from the power feed end.🙁 ). The machine only has two slots and the RT is often in place at the other end. My slot cleaning tool does not get much use, but the vacuum cleaner does a good job.

Hopefully, by now you have ensured that the Tee nut are below the level of the table, and that the bolts or studs are not bottoming through the nut into the bottom of the T slot. (Risk of cracking the top of the |T slot if they do ). Rectify at once.!

Have you checked that the underside of the vice is making contact with the table, all over i.e not warped

Some filing, and possibly bluing and rough scraping needed if it is.

Howard

Sounds like your vise is being clamped to something, just not the table !

Time to have a look to see what.

Vises clamped to milling machines do not move.