• Scam Alert. Members are reminded to NOT send money to buy anything. Don't buy things remote and have it shipped - go get it yourself, pay in person, and take your equipment with you. Scammers have burned people on this forum. Urgency, secrecy, excuses, selling for friend, newish members, FUD, are RED FLAGS. A video conference call is not adequate assurance. Face to face interactions are required. Please report suspicions to the forum admins. Stay Safe - anyone can get scammed.

Tips/Techniques Hold down kit usage

Tips/Techniques
I like low key videos like this, but it's unfortunate that he missed the opportunity to explain how and why table tearout occurs. In so doing, he leaves his viewers at risk of badly damaging the T-Slots on their machine tables.

Anyone not already familiar with the overall issues of compression and tension loading of cast iron might benefit from reading this thread and the ones it links to.

 
I like low key videos like this, but it's unfortunate that he missed the opportunity to explain how and why table tearout occurs. In so doing, he leaves his viewers at risk of badly damaging the T-Slots on their machine tables.

Anyone not already familiar with the overall issues of compression and tension loading of cast iron might benefit from reading this thread and the ones it links to.

I made my own t nuts for a couple different sizes. I followed a couple videos to make them. On one video they staked the bottom of the t nut, so I did as well. In that video they explained the same issue if the bolt jacks up under the t nut your tables done.
 
I made my own t nuts for a couple different sizes. I followed a couple videos to make them. On one video they staked the bottom of the t nut, so I did as well. In that video they explained the same issue if the bolt jacks up under the t nut your tables done.

I don't disagree. What I was complaining about is the missing science that explains WHY it happens.

It's one thing to say that a screw that reaches the bottom of the slot can jack the nut and can easily break the T-slot.

It's another thing to explain that cast iron has very low ultimate tensile strength (fracture/breaking point) compared to steel, but is very strong in compression.

Jacking the lip of the slot tries to bend the lip. It can't bend, so it easily breaks. Tightening a nut up below the lip without anything above the lip also tries to bend the lip so it easily breaks that way too.

A proper clamping setup clamps the lip between the nut and the work which creates a compressive load that cast iron handles very well.

What is missing in every video I have seen is both the science and the objective. The objective is to clamp the lip and the work together in a compressive column. Don't pull up on the lip, bend the lip, or jack it with tensile (bending) loads.

Last, but not least, if you absolutely must clamp an unsupported load, be very mindful of how much force (torque) you use to tighten the clamp. There is no need to gronk on a T-Nut bolt. Even a very modest amount of torque will apply a crap load of force to the clamp.
 
Back
Top