Threads in Wood for machine bolts

[Mike Holbrook]

I have a kinda scary thing I am working on for my new set of hand planes. I have: movable mouth, tote and front handle I need to attach to my plane body. I bought brass machine bolts and threaded nuts....from LV to attach them with.

1) threaded metal bolt method
My plan is to drill a 3/8" hole 5/8" deep ( 3/8" remaining> top of plane), in the movable mouth area, of my plane body. The hole is for a threaded brass nut that the 1/4-20 bolt will fit into. The threaded bolt had a tendency to splinter the top of my piece of soft test wood. I can chisel a little of the edge on the one in my plane and hope the purple heart is tougher but I am a little concerned.

2) tapping wood threads
I bought a LV tapping set too. I could drill a 3/16 hole and tap it with 1/4 threads. I did a test with that method too. It did not splinter as much but I have my doubts about how sturdy those wooden threads would be, even in Purple Heart. Although, LV claims that machine bolts in threaded holes are over twice as strong as screws. The bolt in the movable mouth will be moved in & out every time I adjust the mouth which will certainly wear on wooden threads.

3)tapping for threaded bolt
I am also thinking about trying to locate a 3/8 tap somewhere in town. Then I would have threads in the wood for my threaded bolts. My tapping kit only goes up to 1/4.

I was thinking about using the same threaded bolts & brass machine screws for securing my front handle and tote. I did get a neat little LV hex attachment for a hand drill. It fits in the slot in the brass bolt, for driving the nut into wood. The drill attachment even has a little ball bearing in the side/end of the shaft, sized to snug up inside the 1/4" threads. It makes inserting the bolt straight much easier.

I guess I will do more testing, maybe in some scrap pieces of Ash. I was just hoping some others here have walked these paths and might offer some advice.

[Dale Coons]

haven't done this myself, but have seen it mentioned here on smc several times. Putting CA on the female threads and retapping when dry seems to be a fairly popular way of reinforcement.

[Mike Holbrook]

What is CA? One would put this on previously tapped wooden threads to reinforce them?

[Pam Niedermayer]

[COLOR=#000000][FONT=Comic Sans MS]I have a kinda scary thing I am working on for my new set of hand planes. I have: movable mouth, tote and front handle I need to attach to my plane body. I bought brass machine bolts and threaded nuts....from LV to attach them with....

Don't know what's scary about this; however, I'd recommend contained bolts with nuts driven into the wood for moveable items, much like these. (http://www.leevalley.com/US/hardware/page.aspx?cat=3,43576&p=53225)

Pam

[Jessica Pierce-LaRose]

CA is Cyanoacrylate glue - the various "super glues".

What Pam suggested was also my first thought.

[Mike Holbrook]

Glad to hear others who think the metal nut idea is worth the effort vs threading the wood. I think I may end up using this machine screw & nut system often in other projects I am planing so I am interested in how to perfect it. I am also obsessing about damaging my almost finished plane.

I bought similar but different machine screws & nuts:
http://www.leevalley.com/US/hardware/page.aspx?p=44203&cat=3,41306,41311&ap=1

What is scary is the large amount of surface wood splitting I got trying to drive the threaded bolts into the correct sized drilled hole in test wood. Purple Heart tends to splinter easily. The mouth block area is small and the block needs to sit in it precisely for the plane to work correctly. Do not want to bugger that area up. Seems like it might be even more difficult to get the bolts Pam linked to level in the bottom of the movable mouth area.

I am considering chiseling out a little of the rough wood around the top of the drilled hole so it can't split when I drive the nut into it, filling in the gap with wood filler later. The area is not visible under the block so all that matters is that the movable mouth has a precise seating. I guess I could tap the hole for the 3/8" threads on the bolt, but I would have to find that size tap. Probably I just need to play around with test hard wood until I find a method I am confident want screw up my plane mouth.

I bought a hand tapping kit from LV. I am playing around with using electric hand drill, brace, manual hand drill...to insert the threaded nut. I found it hard to do by hand with a screw driver. It did not want to go in straight and the bolt needs to be seated precisely. I bought a device form LV, designed to drive the nut into the hole and it seems to help:

http://www.leevalley.com/US/hardware/page.aspx?p=65133&cat=3,41306

I (http://www.leevalley.com/US/hardware/page.aspx?p=65133&cat=3,41306)n my first test I tried to drive the nut in by hand with a screw driver, probably not the best idea.

[Rob Lee]

O ye of little faith.... :)

Drilling and tapping wood will work just fine - as long as you have enough threads engaged. Nuts and bolts require an interference fit to function but do not have to be spot on. Bolts are just a long twisted wedge... where the lands of the bolt bear against the long twisted opposing wedge formed by the lands of the tapped hole. The longer the wedge (finer threads) the more surface area (and less force per unit area) you could have - and the greater the force you can apply - until you reach a failure point. Using a bolt tapped into wood can still let the wood move somewhat with causing excessive binding (or cracking) because of the clearances built into the tap...

Where you may have an issue is with wear... but that really depends on the specific application...

Cheers -

Rob

[Thomas Hotchkin]

Mike
When I tap threads in wood I use one size smaller drill bit then tap drill chart recommend. Use a countersink to chamfer hole to prevent splinting. I lube hole with paint thinner, (q-tip works well), before tapping. If it's a small wood part, a clamp will help prevent any splinting. I use CA glue on the threads after tapping and paint thinner has dried. If you can drill your holes with a drillpress and without changing your set up, use drillpress chuck to help center tap handle while threading, wood does not give the same feedback as metal, so for every 90 degrees of feed I turn back 45 degrees. If you do not have room for brass inserts, I have use SS Helcoils with great results, just CA glue then in after installation. Tom

[Mike Holbrook]

Rob, the machine screw/bolt I am working on is for a movable throat on a plane bottom so it will be moved in & out regularly.

I tried inserting a brass nut in a 3/8 hole, the size recommend, in a scrap piece of Ash using my Festool drill. I stripped the single slot off the top of the bolt. Then I tried using my Stanley 813G 12" brace and medium hand pressure, broke another nut. Breaking a nut with the electric drill did not surprise me. I wanted to see how strong they were. I was surprised when I broke the second nut with what I thought was only moderate pressure. I may try Tom's idea of a one size larger hole. I will go down to a 8" Brace too. I need to make a trip to The Depot or Lowes, I will see if they have a 3/8" tap. I am starting to think I might want to use a tougher metal for the nut, also like Tom mentions.

I have a drillpress which I can use to drill & tap the actual plane with once I figure out how to do this without splintering wood or breaking the nuts.

[Jessica Pierce-LaRose]

Driving those brass inserts in harder wood, I've had better luck if I use a large countersink on the hole, as was mentioned above. For driving them, I find I have better luck screwing a bolt into it, and then driving the bolt with a hex socket to sink the insert.

[Mike Holbrook]

Good suggestions Joshua. I just remembered I bought a 1/4" bolt with a head that will take a socket last week when I thought I was going to use threaded nuts that do not have a built in insertion point. I bought a decent countersink set today too.

Even better, I found insert nuts that insert with a large Allen Wrench. These nuts have saw threads that help with insertion and they are made of harder metal. I just ran the same nut into and out of a 2x4 and a piece of Ash with no damage to the nut at all. The spaces in the saw threads prevented any mushrooming in the wood without countersinking. A much better design for an insert nut.

[jerry nazard]

Mike,

You might try making your own threaded inserts out of threaded brass rod. Cut off a short piece of 3/8-16 brass rod, drill and tap it for 10-24, and insert it into a tapped 3/8 hole in your Purple Heart. Use some CA glue to hold the insert in place. Time consuming, but it works.

-Jerry

[Rick Lapp]

I just used this method to attach the grabrails on the top of my boat, based on an article in WoodenBoat in June. The rails are ipe. There was an article in FWW a few years back with a table indicating drill sizes/screw sizes. I used a standard 1/4" tap and my impact driver to drive the screws; tight as a drum! Rick

[Tom Hintz]

When I need to install or repair threads in wood that will be used more than once I use Heli-Coils. You can get kits with the special tap, the coils themselves and a simple installation tool. A dab of epoxy and the inserts never move. I have a story about them on my metal site at the link below. I have used these things in wood for years and have never had an issue with them.

http://www.newmetalworker.com/Reviews/helicoilsrvu.html

[Gary Kman]

To bury a metal nut in wood, an example.

Center drill a 3/4" dowel 1" long. Install a T-nut http://www.leevalley.com/US/hardware/page.aspx?cat=3,43576&p=53225 in the end of it. Drill a 3/4" hole in the work-piece. Apply glue and insert the dowel assembly, t-nut end first in the hole.

[Mike Holbrook]

Wow some very good products and methods brought up in this thread. I love the Heli-Coils. They are a little more expensive to get started but I think well worth the cost. I am doing a little net research trying to find a good place to buy some sort of starter kit that will work well in wood as well as metal. I like the idea of inserting in a wooden dowel too as there is very low risk to the project.

Glad I made this post I was thinking I might get a "buck up" response, instead I have great new methods, tools and fasteners in my arsenal, exactly what I was hoping for..

[Bruce Haugen]

When I need to install or repair threads in wood that will be used more than once I use Heli-Coils...[/url]

I've been using T-nuts for many years, but Heli-Coils never occurred to me, and they would surely be far simpler.

Thanks for the great idea!

[Mike Holbrook]

I am a little confused by the threads thing, apparently there are coarse and fine threads.....My immediate chore is to install threads in wooden planes to receive 1/4-20 bolts/screws. I thought the brass & stainless steel fastners I have would be called machine bolts but I see them referred to as machine screws, this is what Lee Valley calls the ones I have. Mine are brass & stainless, round heads, single slot fasteners which seem to have the same threads. The stainless ones I got at Highland Hardware/Woodworking.

I am trying to figure out which Heil-coils & insertion tools I need to order. I found the Heil-coils searching for Heli-coils 1/4-20 on Amazon (Coarse Thread Repair Kit-12 inserts & two other devices, maybe a tap & insertion tool? $17.19), but there are apparently coarse & fine thread kits. Reading reviews on these devices I find warnings that there are no instructions and no appropriate drill in the kit. One person suggests ordering a 17/64 drill bit as it is needed to drill the hole for the coils. I was hoping to get a little more info on using these in wood. Maybe a suggestion from someone who has used them about: insertion tool(s), taps, thread types, machine screw/machine bolts...

There seem to be "Master" Kits than can run up to $400-$500. I would be interested in a smaller "Master" kit that had inserts and tools for a smaller assortment of fastener sizes appropriate to woodworking, although I kinda doubt there is a woodworking kit. All the information I find on these relates to using them in metal and I am not sure what if any changes need to be made if one intends to use them in hardwood?

[Tom Vanzant]

Mike, the Heli-coil kits shown on Amazon include the tap for the heli-coil, the inserting tool and several heli-coils. The tap-drill needed for the initial hole is not included but is identified in the instructions and is readily available in DIY or hardware stores. You said you were using a 1/4-20 screw so you will need a kit for a 1/4-20 Heli-coil.
If you use a solid threaded insert, I agree with Joshua's driving method. Use a steel screw (1/4-20 may be identified as screw or bolt) with a hex head to install the insert. A brass screw will almost always twist off or break during installation although it's fine for use once the insert is in place.

[Chris Fournier]

Thomas hit the nail on the head. The tap drill should be a size smaller when threading in wood. There is no need for metal inserts in your application if you can get say 3/8" of good wooden threads, unless of course there is a lot of loosening/tightening going on. I have secured bolts in wooden threads for years and in many applications they have withstood 100s of pounds of force without failure over many years. Do a few test taps before you committ.

[Mike Holbrook]

My plane bodies are Purple Heart, which tends to chip and splinter. I am working very hard to make a small piece of Ipe fit perfectly as a movable mouth. Drilling a hole in the smallish recess for the mouth block and then threading that hole could result in damaged wood around the hole. I have done several tests with 2x4 scrap and pieces of Ash, which is the reason for my concerns. Even with a proper, one size smaller hole, tapping and or driving inserts tends to mushroom the wood.

I did find insert nuts that are made of harder steel that have saw threads with gaps which in tests on two different types of wood did not cause the problem. The Heli-coils may cause less issues than the improved nuts I found. I am concerned about trying to thread the Purple Heart itself as it seems more apt to splinter & chip.