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Using a tapered bridge reamer


alan0043

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Hi Everyone,

 

I am starting to get the truck ready for the air hitch. I will be using 4"x4"x1/2" angle steel to support a 1/2" plate that the hitch will sit on top of. It was suggested that I use a tapered bridge reamer to drill the holes in the truck frame. I have done a search on line with no real luck. I also did a search on You Tube. Looking for, how to use a tapered bridge reamer. My question is, do you drill a pilot hole first then go the tapered reamer. What size pilot do I drill. I am planning on using a 9/16" reamer. Also part of the plan is to use six 1/2" grade 8 bolts per side to hold the angle steel. If the bolts seem to small what use would you use ?

 

All input is welcomed,

Al

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Non engineer answer......The strength comes from the clamping force of your bolts, not the shear strength. Thus having the holes a little off is of little consequence. It's more important to use adequate bolts and properly tighten them, than to fuss over getting the holes perfectly round.

 

I'll be staying at a Quality Inn this weekend, so factor that into any wrong answers.....

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Rickeieio, the bolts actually have a lower value in slip critical connections (clamping force) than they do in bearing (bolt body placed in shear).

 

The upside is if a bolt does slip into bearing, it is stronger than when figured as slip critical. The value is the same for both methods when in tension but the bolts in this condition are in shear only, no tension loads.

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Rickeieio, the bolts actually have a lower value in slip critical connections (clamping force) than they do in bearing (bolt body placed in shear).

 

The upside is if a bolt does slip into bearing, it is stronger than when figured as slip critical. The value is the same for both methods when in tension but the bolts in this condition are in shear only, no tension loads.

Thanks for the lesson. When in doubt, I just shoot for overkill, so my fuzzy white a$$ is covered. Never put in 3 bolts when there's room for 4.

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If you are going to use a twist drill, I would recommend using M42 cobalt drill bits. They will stay sharper longer. You will find them at Production Tool or similar tooling outlets. Drill a pilot hole.

 

My personal choice would be to use a Rotobroach style tool. These look like small hole saws, but

more accurate.

 

 

Jeff

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We use round shank reamers from McMaster-Carr https://www.mcmaster.com/#bridge-reamers/=162cs3m 1/2 inch, 5/8 and 3/4. They are pricey but worth their cost in gold. The ETs have over 120 holes in them and require a bit of "finish" reaming putting together welded assemblies. McMaster chart shows you what start hole you need for the reamer you purchase. The ET is mounted on 5/8 plate with 4 x 4 x 1/2 inch angles into the frame. The hitch is held to the plate with eight 5/8 bolts, grade 8. The angles are mounted to the frame with six 3/4 inch bolts, grade 8. Is it an overkill, absolutely, do I fill good about it, absolutely. Am I embarrassed about designing in and recommending an overkill, not a bit.

Could I save money by using bolts with just enough tension and shear rating, sure, about half a six pack's worth.

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  • 2 weeks later...

I'm kinda late to the game, but yea, 12mm 5th wheel holes is medium duty stuff. If you want to stay over 66K GCW then it needs to be 16mm. Yea KW does 17.2 holes for 16mm and 13.2 for 12mm. I just ordered two trucks with custom frame drill. Saved me the work of drilling 84 holes on each truck. That option was worth every penny!

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Hi Everyone,

 

Here is a little update on the truck. The frame is now drilled. Also the angle iron is all drilled and fitted to the truck. Everything bolts up just fine. I had to drill four new holes pre side. The truck will have a total of six holes per side for a grand total of twelve bolts being used. The plan is to use 9/16" grade 8 bolts. The 3/8" steel plate that sit's on top of the angle is also drilled. There is a grand total of twelve 9/16" grade 8 bolts that hold the plate to the angle.

 

Al

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So what did you end up using to drill all of the holes?

 

All the holes on the truck I used a carbide 5/16" bit for the pilot holes and then finished up using a tapered bridge reamer. The holes in the angle iron and the steel plate I drill using high speed steel drill bits.

 

Al

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