Tapped Hole / Machine Screw

[Mike Konobeck]

I have a waterfall bubinga slab that i am going to use as the dining room table top that I need to fix to a base and it is a very dense wood. A thread was going on a while ago on the site because the individual was having a hard time with the screws snapping off. I would like to avoid having to deal with that all together. Has anyone tapped holes and used machine screws instead of the traditional wood screw in dense wood like bubinga. It sounds like you need a special tap for wood. Is that true? Anyone use this tap kit?

http://www.leevalley.com/hardware/page.aspx?c=2&p=40057&cat=3,41306,41330

My plan is to use a stainless pan head or washer type screw in a pre-threaded hole. I need to make sure that the top can float so the head has to have enough surface area. I can't bring myself to drill a large enough hole to use a threaded insert and I think I would still have a problem getting the insert in anyways.

Any help would be greatly appreciated. I don't want to screw this one up. :D

A follow on question is going to come so I might as well ask it now. Is bubinga corrosive? Do I need to consider a special material for the screw or would I be fine with your typical McFeely's stainless (18-8) screw or the like?

[Jason White]

Stainless steel is especially soft and you risk snapping them off in any type of hardwood.

Be sure to pre-drill and use fine-thread screws. Corrosion-resistant (blue in color) Kreg fine-thread pocket screws might be a good choice if they will be hidden. They have a pan head on them and are quite strong.

Jason


I have a waterfall bubinga slab that i am going to use as the dining room table top that I need to fix to a base and it is a very dense wood. A thread was going on a while ago on the site because the individual was having a hard time with the screws snapping off. I would like to avoid having to deal with that all together. Has anyone tapped holes and used machine screws instead of the traditional wood screw in dense wood like bubinga. It sounds like you need a special tap for wood. Is that true? Anyone use this tap kit?

http://www.leevalley.com/hardware/page.aspx?c=2&p=40057&cat=3,41306,41330

My plan is to use a stainless pan head or washer type screw in a pre-threaded hole. I need to make sure that the top can float so the head has to have enough surface area. I can't bring myself to drill a large enough hole to use a threaded insert and I think I would still have a problem getting the insert in anyways.

Any help would be greatly appreciated. I don't want to screw this one up. :D

A follow on question is going to come so I might as well ask it now. Is bubinga corrosive? Do I need to consider a special material for the screw or would I be fine with your typical McFeely's stainless (18-8) screw or the like?

[Grant Wilkinson]

I've used the LV kit on several projects and it works a treat. On the last few, after I cut the threads, I flooded them with thin CA, let it dry well, and cut again. The threads were super crisp.

[Jamie Buxton]

Yes, you can drill and tap hardwood for a machine screw, just like it was plastic. I do it all the time. You should be tapping into face grain, not end grain. Use a conventional tap; no special thing is necessary. I'd aim at getting several screw diameter's worth of threads in the wood.

Here's a thread about a 9' dining table I built a couple years ago. http://www.sawmillcreek.org/showthread.php?t=97018 The bases fasten to the top with bolts that thread into holes tapped directly into the top. IIRC, the bolts were half-inch, and the tapped hole was about 1 1/2" deep.

To make yourself feel more comfortable with the procedure, try it in an offcut. Get several diameter's worth of threads in bubinga, and you won't be able to pull the screw out with a hammer.

[Tom Veatch]

Has anyone tapped holes and used machine screws instead of the traditional wood screw in dense wood like bubinga. It sounds like you need a special tap for wood.


I've used tapped holes and machine screws in various hardwoods and even in plywood. Maybe it's just because I didn't know any better, but it's worked well for me using the standard taps and drill sizes for tapped holes in metal. You're not going to get the same load capacity in wood as you will in metal, of course.

[Mike Konobeck]

Thanks guys! I only have 1 1/8 thick top so it is kind of thin but only 72x40 so nothing like that 9' monster top Jamie did. I am nervous about the table top twisting over time so I am going to have to put more holes in the bottom of the table than I care to. I have a piece of regular bubinga sitting on my rack at it has done some crazy things.

Jamie, Nice work on that table! Very creative way to surface. I took the easy way out and had a local cabinet shop with a 50"+ Timesaver help me flatten it out. A sander is not a replacement for a jointer/planer but it actually did a nice job. They did get a little carried away with a pass or two and I did shed a few tears but it turned out ok. Just have to get the base done (through mortises are my nemesis).