Drilling holes in the TT's frame question

[NanciL]

I am going to be drilling some 1/2" diameter holes in my trailer frame ,(the I beam) for some eye bolts for hurricane tie downs.
My question for any one that has done this or drilled through any steel is ; Would you first drill a smaller diameter hole, or go right at it with the 1/2" bit?

Jack L

[NanciL]

I had some extra time today, so I drilled the first three holes on one side and installed the cable tie downs.
I was quite surprised at how easy the drilling was.
First of all, I found out that the "I" beams are not structural "I" beams but very flimsy. I don't know what the thickness of the web where I drilled is, but I know it is thin.
I drilled a 1/4" pilot hole at a slow speed and then used the 1/2" to enlarge it and both my drill bits were old ones.

I have three more to go on the other side, and it will be done.

Jack l

[JBarca]

I'll add a few things. I have never had to deal with a TT in a hurricane, but I have had to deal with camper frames. I'll pass these ideas along to help the cause.

I myself would not use a beam clamp or any other clamp on the lower flange of an "camper" I beam. These camper I beams are so thin you can damage that lower flange real easy pulling with hurricane forces on it. Even a 18" crescent wrench can do damage pulling on it. Yes, they are that flimsy. No problem cold working a bent flange back straight .

The way an I beam works is the top and bottom flanges carry the load of the beam. One in tension the other in compression. They change loading depending on which way the force is applied. The web in the middle prevents the flanges from buckling sideways not really carrying the majority of the load that the flanges do. Once one of the flanges is distorted, it can then be the new weak point in the beam. You end up towing on a bad highway with potholes and the frame is stressed from the potholes, it will find that new weak spot and start the beam bending in that location if the impact is hard or multiple enough.

Do not drill holes real close to the edges of the flanges like it will be close to breakthrough as that will create a stress riser in that load carrying area.

Folks do talk about the big hole where the slide arm come through, but that is in the web and most times a reinforcement plate is welded around that hole to help compensate for the hole being there. Again to help not buckle the beam is the need.

What makes the I beam stronger faster is the flange dimensions and the total height of the beam as opposed to just going thicker steel. The farther apart the flanges are, the stronger the beam. A 10" MH beam is stronger then an 8" MH beam given all the thickness, flange widths and yield stress rating are the same. The increased height of the beam in the bending direction increases the section modulus used in the stress calculations much faster then increasing section thicknesses.

Many of the I beam frames are made out a high strength low carbon steel. A572-50 or A529-50 which is 50 ksi yield steel. It is a step up from the average A36 softer steels. However I have used standard high speed steel bits to drill it successfully if your going to drill it. Cobalt bits work too just heads up they may snap faster if you do not hold the drill motor steady. Start small and increase the bit size with lube

After thinking through all this, I do agree if you can, go over the A frame Tongue and the rear bumper if yours has any structure to it. Some of the rear bumpers are not very strong.

The poster who added to put a cable through the spring hangers is good too. That can give you 6 locations at the wheels area.

Hope this helps

John

[_1nobby]

Passin Thru wrote:
Actually I am an aviation airframe mech To drill hard steel frames, Us a 5/16 pilot

5/16?

In aluminum, maybe.

But even then....that's pretty big for a starter hole.

[Lynnmor]

I have never seen a trailer frame made of steel that is very hard. Any drill bit, better than the extremely cheap junk, will cut it just fine.

[profdant139]

I start with a sharp center punch -- make a good divot where you want to drill. Then start with an eighth inch bit. Go very slow -- the goal is to cut long twisty waste, not little shards. Then step up, as slowly as possible. Wear good googles -- those steel fragments do not feel good when they get in your eyes.

I keep a strong magnet handy to pick up the fragments. Makes clean-up a lot easier.

Harbor Freight sells tapered bits -- they work pretty well on mild steel but not on really hard steel.

[time2roll]

Drill baby, drill. Just stay away from other items and holes as much as possible. Use some lube for best drilling experience.

Half inch hole is nothing compared to the slots carved into my frame for the slide. And yes I have drilled my frame plenty and some at half inch.

[Passin_Thru]

Actually I am an aviation airframe mech To drill hard steel frames, Us a 5/16 pilot followed by step drills moving up 1/4 at a time. When You finish the hole, use a larger bit to round off or chamfer (deburr) the edges of the hole thus preventing stress cracking. Use hard grade 8 bolts and torque to the proper torque and flat washers to prevent stress on each side of the hole.

[westend]

1/2" seems like a fairly large hole to accommodate hardware. You could probably choose a smaller diameter and have a lot of tensile strength left over with the hardware. I'm with others about the beam clamps but I have no idea about the intricacies of FL tie down rules. I'd assume that only a cursory inspection would be done and if the unit had some sort of protection against lifting in hurricane winds, that should suffice.

To answer the stated question: Yes, starting with a smaller bit and working up to larger diameters is the best way. If the steel in the frame proved to be very hard, I'd suggest to use a stepped bit of good quality. They seem to remove material easier than straight bits in some situations. Further suggestions: Keep bit speed low and use cutting fluid to keep bit temps down.

[gmw_photos]

I'm curious what you are going to anchor to into the ground ?

I would agree that a couple sets of ancra motorcycle tiedowns, or even just some 2" or 3" ratchet straps would work. But like the others have said, one would think after this riding out a hurricane, it's gonna be an insurance write-off anyway.

[prichardson]

If you must have it remain in a hurricanes way Hannibal has best idea on attachment points. No drilling required. Front and back would be enough; but if you really want a third strap point use a cable thru a spring perch.

[NanciL]

Durb wrote:
Unless you have split point drill bits the half inch bit isn't going to do well starting a hole. I would drill a pilot hole large enough to overcome the non cutting center portion of your drill bit (assuming non split point). This will help with bit walk when starting the hole. Too large of a pilot hole will cause the 1/2" bit to grab when enlarging the hole.

Thank you,

Much appreciated

jack L

[Retired_JSO]

Should read the Statute although it won’t help much.

[Hannibal]

I use heavy duty motorcycle straps at the tongue and rear bumper and ground anchors. Same for the boat and trailer.

[mosseater]

I don't know about the rest of you, but I tried drilling a starter hole for a self tapper, and conduit, and my frame is hard like woodpecker lips. I ended up using Caddy Strap clamps, since all I was doing was attaching the smurf tube containing the back up light wiring. I'm no stranger to drilling difficult holes. This would take something hard to get through, carbide, cobalt, etc.