Your preferred hold down fasteners?

[Janger]

Question for the forum - what size hold down bolts and ready rod do you use on your mill generally? Maybe the question should be what size is your clamping kit?

 

[Brent H]

Hey John,

When I bought my mill i got a bit lucky as the seller included what worked out to 1.5 clamping kits. I received two trays, one complete with all the wedges and clamps and bolts etc and one that only contained the bolts and a couple coupler nuts. Both these sets are 1/2" and seem well suited for a standard Bridgeport or BP clone.

At work we have a 3/8 set for a smaller mill (Busy Bee 600). I also have some parts in the 3/8" at home for the lathe face plate

 

[YYCHM]

Doesn't the table slot size govern this for the most part?

 

[RobinHood]

Complete set 1/2” on the BP mill
Complete set 3/8” from tool buy (also used on the mill and anywhere else it is required and it fits)
Some M10 from the Deckels
Some Whitworth from the Clarkson T&CG

 

[6.5 Fan]

My hold down set is 3/8 that's what fits the t slots.

 

[Dabbler]

I have 2.75 sets of 1/2" hold downs. On that small mill, I enlarged the T slots .030 in order to use the larger 1/2" studs.

 

[Tom Kitta]

I have roughly 2 sets of 1/2 hold downs for both large mills and few smaller 3/8 for smaller stuff such as a baby mill and small drill press.

 

[YYCHM]

I'm curious as to why you posed this question? I have a 1/2" clamping kit for my mill and had to make some custom 1/2" T-Nuts for my RT. The face plate I slotted for my lathe is 3/8".

 

[Hruul]

I don't have a mill but the t-slots on the milling attachment I have for my lathe appears to be a 12mm t-slot (widest/bottom of the t-nut). In the process of making some T-nuts for it so I can quit using the hex head bolts that I filed down to fit currently.

 

[Janger]

I'm surprised at the number of 1/2" votes - clear winner. I thought it would be 3/8 or maybe M10 (what I have). I use a lot of 3/8 t-nuts and regular 3/8 bolts though too.

 

[Dabbler]

The majority of machines I used have all used 1/2 " stud kits. Even my little mill only need a little tweak to use them. And you need a really big mill to need 5/8" ones.

 

[Chipper5783]

Sized to the machine. Two 1/2" kits for the mid sized mills, a 3/8 kit for the little Maho. I've made a few custom Tee nuts for nearly every Tee slot ( because when you actually measure them, every one is different) - and sometimes an under sized stud or bolt is needed (3/8" on the larger mills, a 1/4" bolt in the middle of a part etc.).

 

[PeterT]

I have some metric tooling like RT where the casting lug dictates M# fastener therefore the T-nut must match, even though the table slot itself is capable of slightly larger. Same thing with some fixture plates I made for bolting into chucks, but I can bolt the plates themselves down to table. I use these Bessey style for setups because very fast to set up as long as the part isn't too high. Model 500 = 1/2" model 375 = 3/8". So the answer for me at least is: 'it depends' and a range.

I think most Asian Bridgeport clones have T-slot dimensions milled to Imp standards to mimic N-Am Bridgeport's (as opposed to actually being metric but close enough that the IMP works). I've never been able to verify. Anyways it pays to have a few different kinds kicking around but more dictated by the tooling & fixtures you strap on.

 

[PeterT]

Side note - unfortunately this sort of question comes up too frequently. How do I put Humpty Dumpty back together again?
1/2" bolts are what like 7-14 ksi tension depending on the grade. Hobby grade cast iron is no match for excess gronk force like what a big commercial machine could withstand. You don't want things to move under machining forces especially interrupted cuts. But there is also no sense going nutty on clamping pressures. I've never actually seen a torque rating for mill tables, have any of you?

 

[RobinHood]

Not sure if this is the type info you are looking for Peter. Here is a Torque table for aluminum extrusion T-Slots. I have not found one for CI tables yet.

For a 5/16 T-nut it is 20 ft-lbs, so not a whole lot.

Here is the link to their website: https://faztek.net/technical.html