PDA

View Full Version : t bolts



kjbllc
01-15-2010, 07:34 AM
I looked through the archives about t bolts. I need to get some 3/4 and 5/8/. The ones I see for sale are hardened. On some of the posts I read I see that some people make them from regular steel and counter sink through a flat piece of steel.


Do they need to be hardened, or does it depend on how much torque you are putting on it.
They will be used on a hardinge horizontal tm, and a 3 hp gear drive solberga drill press.

http://i254.photobucket.com/albums/hh92/kjbllc/drillclean003.jpg

on another note, I can't seem to get the drill press to lock into auto drive ( if that is what you call it) I think I can lock the handle into two positions but neither one will drill auto.
again thanks for any help with this. kevin

bob ward
01-15-2010, 08:15 AM
Hardened hold down bolts are good for industry, they stand up to wear and tear a lot better. For home use mild steel is fine.

If you make your own tee nuts don't forget to stake/damage the threads on the underside to stop the bolt going right through.

kjbllc
01-15-2010, 08:22 AM
Hardened hold down bolts are good for industry, they stand up to wear and tear a lot better. For home use mild steel is fine.

If you make your own tee nuts don't forget to stake/damage the threads on the underside to stop the bolt going right through.


Thanks for the reply, I don't know quite what you mean by stake/damage. Is that removing the threads so they don't rub on the sides of the t slot? Or making the the head larger so it doesn't slip through.
thanks kevin

EVguru
01-15-2010, 08:40 AM
If the top nut binds on the stud, then the stud could get screwed through the T nut and jack it up against the underside of the T slot. Since cast Iron doesn't have much strength in tension, it's actually possible to break the slot!

You stake the T nut, so the stud won't screw through.

Carld
01-15-2010, 08:44 AM
He means to distort the thread with a center punch to keep the bolt from backing out. You can lock it in with Locktite.

If you make your own hold down bolts use all thread, it makes it much easier to make them and I suggest the Locktite because you can replace the all thread easier when it's damaged.

kjbllc
01-15-2010, 08:48 AM
Thanks I see what you are talking about now, don't know the lingo, I am just learning about this stuff. The all thread sounds like a good way to go. thanks kevin

kjbllc
01-15-2010, 08:57 AM
How much torque do you use to tighten the t nuts, if too tight you would also break the t-slot?

Carld
01-15-2010, 09:09 AM
I wouldn't use an impact wrench but the standard box wrench that fits the nut would be ok if you don't exceed the recommended torque of the thread size. Look in a chart and torque the bolt with a torque wrench and then try the feel with the box wrench and when you can tighten the bolt with the wrench and test it with the torque wrench and it's close your good to go.

It's developing a feel that is the trick. Use a torque wrench to get used to it.

At one shop I worked there was a machinist that was very strong. He broke the T slots on a BridgePort by over torquing when the T nuts were at the very end of the slots. The shop owner was very upset with him for a long time.

J Tiers
01-15-2010, 09:15 AM
Well, for a t-BOLT it isn't really relevant, as with a t-bolt, the head fits the slot, and there is no separate threaded shank that can screw thriough the "head" and cause trouble.

The damaged thread issue is mostly for a t-NUT, which can break the slot out. In that case, you can either burr up the last thread or so on the nut, or deform the thread on the threaded rod so that it can't screw clear through.

Wherever possible, use a setup where the work, or fixture, tightens down directly on the table right over the t-nut. That way all the forces are inside the metal. If you have a long stud up to a hold-down bar, out somewhere far from the work, you can break out the slot. Move the stud closer and the lever arm will help you use less force, as well as getting support from teh work to help reduce force on teh slot. Or change the setup if that isn't possible.

As for hardening.......

I have seen lots of stern warnings to never use common all-thread for hold-downs..... And I consider them silly. I have been using common harware store all-thread for years, with never a problem and no expectation of one.

In fact it may be SAFER, since if you get to trying to torque down THAT hard to hold something where maybe you don't have enough holding the part, the threads will probably strip, or the rod fail in tension as you tighten. It tends to fail "soft", with ample warning.

With hardened studs, you may have the whole thing break and throw pieces at you with little or no warning, possibly during the cut. There is hardly any elongation with hardened studs vs common all-thread, the studs just crack suddenly.

And, if you really need to tighten down that hard, you probably need to consider some auxiliary 'stops" etc to prevent work sliding..... Or you are expecting too much overall.

Ian B
01-15-2010, 10:02 AM
Tee nuts and studs are generally handier than tee bolts - with a nut, you can slide them under work / vises etc when you need to add an extra holddown. As others have said, make sure the stud can't screw all the way through.

Ian

Frank Ford
01-15-2010, 11:21 AM
JTiers -

I'm with you - I've read the "warnings" but they seem aimed at industry or folks who do much heavier work than I do. While I do use regulation T-bolts, studs and all, I also make some T-bolts out of the appropriate size of carriage bolts and, if needed, a judicious bit of file work:

http://www.frets.com/ForumPix/carriagebolt.jpg

kjbllc
01-15-2010, 03:59 PM
Thanks for all the replies and help. kevin

JTToner
01-15-2010, 11:29 PM
I made mine from 1018 and no problems, 5/8" dia. for the mill and 1/2" for my R/T.
Johnny

strokersix
01-16-2010, 08:07 AM
If you are going to use allthread I highly recommend alloy instead of regular hardware store allthread.

One source: http://www.greenbaymfgco.com/catalog.php?cat=7

You will be much happier in the long run. Fewer dinged threads and stretched studs. Nuts spin on freely. You can feel the difference when torquing the nut. The alloy will cinch down nicely. The low carbon will feel soft and you are not sure whether the stud is yielding or you've caught swarf under your clamp or?

My 8x36 vertical mill has big enough slots to use 1/2 inch studs but I don't own any. I use 3/8 and have always had enough clamping force available with alloy studs.