Tee Slots and clamping

[JimM]

Hi guys

I need some advice about the best way to clamp down my vice on the milling machine.

I have an old Elliott Juniormil which although it has a 28" x 7" table has ridiculously small tee slots, the narrowest part being only 5/16 wide.

I've knocked up some tee nuts but when used with the 1/4" studs they just don't look meaty enough to hold my 5" vice securely. I can see a couple of way round this but not sure what the best method would be from.....

1. Go with the 1/4" studs and just use a couple of larger washers to spread the load.

2. Use 5/16" studs but with flat nuts as opposed to T nuts. Problem with this is that there wouldn't be a whole lot of depth on the flat nut to thread into. The other option would be 5/16" Tee bolt, which would be OK for the vice but I lose some flexibility when it comes to other clamping needs.

3. Use 3/8" studs with a flat nut - obviously I'd need to turn down the area where the narrow part of the t slot would be and would have to slide the assembly in as a whole from the end of the slot. Was thinking that the advantage of this over number 2 would be that the stud couldn't be pulled out of the slot.

So what would the collective wisdom suggest ??

Thanks

Jim

 

[bentprop]

Hi Jim,on the face of it,no.3 would seem to be the best option.Unfortunately,it still means your hold-down power is compromised by the narrow part of the stud.
So you might as well use 5/16th t-bolts.Use high-tensile if you can get them.You could still use t-nuts with 1/4 studs for smaller jobs.
Fwiw,my clamping kit uses 14mm studs,and even they can work loose with an interrupted cut.So care is still needed to make sure everything is snug.

 

[Twmaster]

Jim,

The table on my Taig has very small slots like yours. I usually use two main hold downs on the vise near the rear of the table. I then put two more little things on each side of the vise at the front of the table to keep the vise from rotating.

Unfortunately my milling machine and tooling is all crated up awaiting my move so no piccies.

 

[rake60]

You might consider making some T-Bolts.
Of course you could BUY them, but where would the fun be in that?
They would still need to be modified a bit.

Rick

 

[mklotz]

How about bolting your vise to a 3/4" or so steel plate and then bolting said plate to mill table with a bunch of the bolts that fit the existing slots?

That would spread the stress over a larger number of the weaker bolts.

 

[Stan]

My Benchmaster mill only has 3/8" slots so I use a combination of T bolts and T nuts. Vises and rotary table get T bolts and most jobs clamped to the table get T nuts and 5/16" studs.

A 1/4" stud in grade 8 will hold a lot if the clamp is used properly. Since vises usually have holes big enough for 1/2" studs, make shoulder washers to fit the hole and the stud for better clamping.

 

[rleete]

A single 1/4-20 bolt (grade 2) will provide over 700 pounds of clamping force. Better grades will provide even more. You only need to get some decent threaded rod or bolts, and not overtorque.

I'm willing to bet that the T-slots are the weakest link, not the threads.

 

[starbolin]

I don't see a problem with 5/16 studs and flat nuts. Have various lathe attachments with that arrangement and haven't had a problem with pullout. I also like mklotz's idea of a subplate.

Whatever you do make sure the top nuts have a large enough flange to engage the ears on the vice. Don't depend on hardware-store washers to take the load. I've seen several examples of vices and rotabs where the nut didn't properly transfer force to the mounts. What happens is the washer eventually loosen, the operator keeps re-tightening, and eventually something fails, either the stud bends or the threads strip or both.

 

[deverett]

Jim

I know this is quite an old topic, but I've been away for a while...

You being a Brit (by the sound of things) will have heard of George H Thomas and his workshop wisdom. In the description of making his clamping system, GHT made Tee nuts threaded 5/16" BSW. The bolt was 3/8" diameter, stepped down to 5/16" where it screwed into the Tee nut. These he used on his Tom Senior M1 milling machine.

May not sound good engineering practice, but if that was good enough for the Master, then I'm sure it would be good enough for the Pupil.

He also had some Tee nuts that came above the table top to accept 3/8" bolts but were slotted to fit the narrow stem of the Tee in the table.

If you want further info, I can look up the relevant articles in ME.

Dave
The Emerald Isle

 

[Omnimill]

I'd go with 5/16" Shop bought (hopefully High Tensile) T bolts.

Vic.

 

[JimM]

Hi all

Thanks for all the suggestions and I have a little update

As I had gone to the effort of making the T-Nuts I thought I might as well give them a try. For use with the vice I made some top hat style washers (used brim facing up) so that there was a bit more meat around the stud and used some threaded HSS for the stud itself. Only had a little use to date but seems to be holding well.

When I get a chance I will get some 5/16 T-bolts as feel this would be just that bit more secure, just need to find a UK supplier !

Cheers

Jim