Drill and Tap the frame rails

[Brianna]

Has anyone drilled/tapped small holes into the frame rails to mount stuff?
For example: relocate your water pump, add components to the battery bay, etc.

Any tips, advice, warnings you would like to share?

[Firedog53]

True "frame rails" are typically off limits for drilling. There's all kinds of fancy things going on with the rails like strength, Resisting Bending Moment and other terms I don't understand. I do understand the manufacturer telling me NOT to drill the frame and flanges because bad things happen.
Maybe adding brackets and bolting things would be a better approach...

[Mile Marker 42]

Originally Posted by Brianna

Has anyone drilled/tapped small holes into the frame rails to mount stuff?
For example: relocate your water pump, add components to the battery bay, etc.

Any tips, advice, warnings you would like to share?

People drill small holes all the time. Just make sure to check the other side of the frame rail before drilling. You'd hate to drill into a brake line or something:(

[richard5933]

Check out any truck supply house and there are loads of ways to clamp things to frame rails to avoid drilling.

[Alpine36]

We did it all the time in 30 some years of upfitting utility trucks.
A couple rules of thumb, never drill a frame flange (the horizontal upper and lower part of the frame rails) and make sure your holes are no closer than 1.5" to the frame flanges. I wouldn't recommend tapping the frame. Use quality sharp cobalt drill bits, flange bolts, Esna nuts and flat washers. Make sure to de-burr and paint the holes before assembly and you'll be just fine. This procedure is used by most truck up fitters to install service bodies, aerial devices, outriggers, cranes etc using both aforementioned nut/bolt method or huck bolts.

[Brianna]

Thanks for all the input.

[KanzKran]

Through-drill cleanly, no larger than needed, deburr, and nut and bolt to attach something, as stated. Stay away from the flanges, the further the better. In most cases, the center of the frame rail is the lowest stress part except for shear, but shear stress is usually low relative to bending stresses.

[Mark_K5LXP]

Something I've done for various interior and exterior mounting is construction adhesive. Glue a bracket or mounting plate to just about any surface with that stuff and it's as good or better than fasteners. No compromise to the underlying substrate. I've stuck stuff to frames and body panels this way and you don't need access to the opposite side as you would with nut and bolt. No different than how many cars are put together these days, it works.

Mark B.
Albuquerque, NM

[Ljwt330]

Originally Posted by Mark_K5LXP

Something I've done for various interior and exterior mounting is construction adhesive. Glue a bracket or mounting plate to just about any surface with that stuff and it's as good or better than fasteners. No compromise to the underlying substrate. I've stuck stuff to frames and body panels this way and you don't need access to the opposite side as you would with nut and bolt. No different than how many cars are put together these days, it works.

Mark B.
Albuquerque, NM

Would I be correct in assuming that if using an adhesive, it is mandatory that the adhesive be applied to bare metal of the frame rail?

[twinboat]

I have drilled lots of chassis to bolt things on, back in my working life, no big deal.

Bolts and nuts are easy if you can access the inside of the rail but threading the hole will work fine too.

Its not rocket science.

[Brianna]

What a great forum.

[Piros1]

Originally Posted by Alpine36

We did it all the time in 30 some years of upfitting utility trucks.
A couple rules of thumb, never drill a frame flange (the horizontal upper and lower part of the frame rails) and make sure your holes are no closer than 1.5" to the frame flanges. I wouldn't recommend tapping the frame. Use quality sharp cobalt drill bits, flange bolts, Esna nuts and flat washers. Make sure to de-burr and paint the holes before assembly and you'll be just fine. This procedure is used by most truck up fitters to install service bodies, aerial devices, outriggers, cranes etc using both aforementioned nut/bolt method or huck bolts.

Exactly what I have seen and been told in truck world. I will add obviously you don’t want several holes close together.

[Alpine36]

Originally Posted by Piros1

Exactly what I have seen and been told in truck world. I will add obviously you don’t want several holes close together.

That's a good point. We never put any holes closer than 2" spacing. I'd be very hesitant to tap the frame, as it could cause problems. We always used specialty flange bolts rated for the application. You want an exact fit between the o.d.shoulder of the bolt and the I.d.diameter of the hole. Under no circumstances did we allow any bolt threads to make contact with the frame hole. In simple terms, your looking for equal clamping force with no stress on the frame holes. Now of course, we were building 65' bucket trucks, cranes, pulling/tensioning equipment, digger derricks etc....Those subframe and A-frame outrigger mounts put unbelievable amounts of stress on the chassis frame. If you're simply mounting a battery box or light weight component I guess you could drill and tap, but I've never seen it done. Ask yourself, have you ever seen a chassis suspension or structural component attached by tapping a hole in the frame? They're either huck bolted, thru bolted or riveted for good reason.

[richard5933]

Isn't one of the big issues getting the frame too hot and causing it to lose strength?

There's a reason commercial trucking companies use large U-bolts and clamps to mount equipment if there are not mounting holes in the frame rails if they are marked "drill no holes".