Pilotholes in softwood endgrain

[RogerD]

I am about to plunge 6" three eighths dia. coach screws into one and a half inch thick 'red pine' endgrain. The thread profile is aggressive and thick, So far, my best advice to date is - "Drill a long thinnish hole and keep trying it , if it jams, widen the hole until it goes in. You'll soon get the right fit by trial and error.....", OR - "Measure the diameter of the core of the threaded section and drill that diameter hole, but no larger." (obviously). I'd have thought that a certain amount of compression was essential to get a really firm bite without splitting the wood - I favour the idea of drilling out that part occupied by the shank a bit undersize, and the thread a bit under the core diameter. These will secure cross beams to the legs of my new workbench so there'll be a lot of angular stresses.
Wise thoughts please,

Thanks,

R

 

[MikeW]

Welcome, Roger!

Personally I would use bolts with the nuts recessed into a pocket a minimum of 3" from the end of the cross beams.

If you do use screws, test on some scrap. I wouldn't go much below the root diameter of the screws if any at all.

Take care, Mike

 

[A_n_g_e_l_a]

Given the high loading on the joint I might be tempted to put in a large diameter (25mm +) cross dowel in the pine since you have already bought the coach bolts.

Locate the dowel such that the business end of the coach bolt will have some cross grain to purchase on. That will tend to prevent the end grain suffering shear failure if you try to tighten things up too much.

But in this situation I would choose to use plain bolts and a metal threaded cross dowels.

 

[Paul Chapman]

Hi Roger,

I don't think your idea sounds very good at all. I'd go with MikeW's suggestion of recessed nuts or use something like these cross dowels - they make a very firm fixing http://www.woodfit.com/product_info.php ... +30mm+long

And welcome to the forum.

Cheers :wink:

Paul

 

[woodbloke]

Some excellent advice given so far. With coach screws a 25mm cross grain dowel, as has been suggested earlier, will give far more 'bite' than just trying to screw into end grain.....it's rather like trying to screw a thread into the end of a bunch of spaghetti held in your hand (the thread is reluctant to draw itself into the spag) Try it with the thread at 90deg to the spag at it goes in without any trouble - Rob

 

[RogerD]

Thankyou everyone for your valuable wisdom. I would have been a lot happier to pursue this cross dowel on captive nut approach, had I not been faithfully following John White's directions for his 'New-Fangled Workbench' - Fine Woodworking Dec'99. Instinctively, I sensed the fistful of spaghetti syndrome that Woodbloke speaks of as soon as I saw the threads. White says the thing is '-rock steady' and to 'drill pilot holes' - so I think 'OK.... I'll try it- but how big!?' I suspect that I'll retro-fit cross dowels in the fulness of time, but I've got these SIXTEEN coach screws - so , in view of THAT , my options -right now - are kinda resricted. So, bear with me....Fat holes or Thin???

Cheers!

R

 

[Paul Chapman]

Even though you've bought them, if it were me I still wouldn't use them. But if you want to, I'd drill the holes the same size as the solid piece of the screws. All you want left after drilling is wood for the actual thread to cut into. You might have to use two or three drill bits so that the holes are tapered to approximately match the tapers on the screws. If you drill narrow holes, the screw will just force the spare wood out of the way and, as it's end grain, it might split. If you have some spare wood try it out on that.

Good luck :wink:

Paul

 

[MikeW]

Hi Roger,

John White is a pretty approachable person. If you are registered on the Taunton web iste, you can go directly to his messages flder and ask him:

http://forums.taunton.com/fw-experts/me ... opfolder=6

If I were doing this, like mentioned, use some scraps to test size and proceedure. I think you'll find the nominal root size into the end-grain piece will afford the best holding without risk of splitting the thick cross pieces.

It's been a while since I looked at his bench, but I suspect the hole through the leg is the size of the unthreaded portion (if there is one) to allow it to turn unimpeded?

Take care, Mike

 

[RogerD]

Thankyou very much Paul and Mike W. What you say exactly fits my instincts about this.
Tomorrow I'll approach the supplier of the screws and ask to exchange them for cross dowels. In the meantime I'll rattle Taunton's bars AGAIN -the 'ask an expert' site for John has been down for a while now. The one you gave me Mike, is 'cannot be displayed'
I've learnt a lot just through this little exchange. (My theory is that learning something new in retirement will keep me sharp - so far I'm running to keep up - it's what I worked all those years for!!!)

Thanks again!

R[/i]