Screws stripping out pilot holes

What kind, options, etc.

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Antler24
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Screws stripping out pilot holes

Post by Antler24 »

So another newbie dilemma here. Im working on frame 4 and about to glue/screw the whole thing together. Figured Id test a few screws on some scrap first, #8 3/4" silicon bronze screws. Drilled pilot, drive first screw in and it just keeps spinning. Step down to a 3/32 bit and set the clutch setting down to 4 (goes up to 22), drive next screw and same thing, it starts to tighten and then you can feel the wood give and the screw spins freely. So then I dont even countersink, just drive a screw through the ply into the mahogany and no difference. Screw goes flush with the ply and starts to tighten then spins freely in the mohogany.

What am I doing wrong?

TAB
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Re: Screws stripping out pilot holes

Post by TAB »

Have you tried with out the clutch? For hardwoods i found my inpact driver works far better for getting almost to the emd then a bit brace or a screw driver i cam get a wrench on for extra torque to finish it.

Antler24
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Re: Screws stripping out pilot holes

Post by Antler24 »

I dont think I need more torque. I keeping stripping the holes not the screws

hoodman
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Re: Screws stripping out pilot holes

Post by hoodman »

Your attaching ply to mohogany? What thickness is the ply. 3/4 inch screws seem like a little short maybe.
Matt

Building a Geronimo......!
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Bill Edmundson
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Re: Screws stripping out pilot holes

Post by Bill Edmundson »

Most of my screws were 1".

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
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Antler24
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Re: Screws stripping out pilot holes

Post by Antler24 »

1/4" ply

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Roberta
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Re: Screws stripping out pilot holes

Post by Roberta »

Are you using a tapered counter sunk bit of the correct size for your pilot holes? You may need to set the depth as well. Should be slightly shorter than the screw length. Do some testing in scrap to ensure the proper size and depth.

Roberta.
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

hoodman
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Re: Screws stripping out pilot holes

Post by hoodman »

Are you sure your screws are spinning in the holes or are the heads breaking off?
Matt

Building a Geronimo......!
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Roberta
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Re: Screws stripping out pilot holes

Post by Roberta »

Good point! An improperly drilled pilot hole will jam a screw and a peppy driver can snap the head right off. In addition to a pilot hole, some builders swipe a little soap on the screws to lubricate them to ease them in.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

Antler24
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Re: Screws stripping out pilot holes

Post by Antler24 »

Nope they are definitely spinning freely in the wood. I can easily back the screws out and use them again, they are undamaged.

Im using a dewalt #8 countersink bit that drills both the head and shank of the screw, and you can swap out bits for the screws thread. I set the bit depth to about an 1/8" shorter than the screw. The Boatbuilding with Plywood book suggests a 7/64 bit, which I started with, then tried a 3/32, and then just drove a couple down without even predrilling.

danman
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Re: Screws stripping out pilot holes

Post by danman »

Antler24 wrote:
Wed Aug 26, 2020 7:17 pm
Nope they are definitely spinning freely in the wood. I can easily back the screws out and use them again, they are undamaged.

Im using a dewalt #8 countersink bit that drills both the head and shank of the screw, and you can swap out bits for the screws thread. I set the bit depth to about an 1/8" shorter than the screw. The Boatbuilding with Plywood book suggests a 7/64 bit, which I started with, then tried a 3/32, and then just drove a couple down without even predrilling.
Mahogany is a real soft wood. You'd be better off using a tapered bit to pre-drill. And go real easy you, just need it to hold till the epoxy cures.

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chugalug
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Re: Screws stripping out pilot holes

Post by chugalug »

I put all my screws in by hand instead of power tool.Had a t-handle with bit Could torque down to compress ply easier and could tell when to stop.Lubed screws with spit or wax from toilet bowl wax ring.Did predrill holes.could use drill and stop earlier and torque down by hand.
Working on regular-sized Bo-Jest


"If it's not crooked,It's not mine

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acflynn
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Re: Screws stripping out pilot holes

Post by acflynn »

I agree with danman - either a smaller or tapered bit for the pre-drill. Also it's been recommended not to countersink plywood ahead of time. I was given the advice that with plywood, you do not want to countersink the hole, only pre-drill. The screw head should capture the ply layers and self-countersink. For hardwood you do want to drill and countersink.

My issue with the SB screws was either stripping the frearson heads or snapping the heads off with the impact driver. I now use wax on my screws (most of which works itself out) during the sinking and rarely now ruin a screw.

I don't think it's the wood. I am using Sapele mahogany, which is harder than White Oak on the janka scale, but much harder than both African and Honduran mahogany. But even the softest mahogany should be at least 50% harder than Douglas Fir, among the hardest of the "softwoods", so I'm leaning towards the pilot hole size and depth.
Slowly building a Mist Miss in the Arizona desert

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