I'm thinking of tapping some threads for machine screws in hardwood, mainly mesquite and maple....maybe oak and walnut, too.  Only on the face or edge grain. Though, doing it in end grain might be tried. Has anyone tried it? Any cautions, advice, comments? 

Thanks in advance.

Edited March 1, 20188 yr by Gene Howe

Side and edge grain works well but end grain usually doesn't- at least in the woods I've tried which is mostly oak. Something as dense as mesquite might work for end grain. Mostly what I've done is 1/4 x 20.

 

I've also done 1 x 8 for the lathe headstock- always in face grain.

Edited March 1, 20188 yr by lew

Thinking about end grain...maybe some CA on the threads would toughen them up in less dense wood? 

Would a threaded insert work better?

4 minutes ago, Chips N Dust said:

Would a threaded insert work better?

 

My thoughts too.   If careful the threads can be epoxied also.

Edited March 1, 20188 yr by HandyDan

17 minutes ago, Chips N Dust said:

Would a threaded insert work better?

Probably. But, threading the wood would be faster, and cheaper. Not to mention, experimenting is fun.

Years before i had any steel cross-dowels, i cut and threaded sections of wood dowel to do the same thing.   Can't say now if it was hardwood or soft, but i went all the way through and it was a fairly coarse thread (1/4-20).   In really hard wood, you may be better off with a 3 flute cutter and the same rules apply for wood as metal - lube it up some and back out to clear swarf from time to time.   I vaguely recall doing some smaller threads, but that brain cell is on vacation right now.

Thanks @p_toad. Didn't think of lubing it. I'm planning using 3/8-20 screws. Lube may be really helpful.

Threading a dowel is an idea that opens up more possibilities. 

Hey Gene, if someone else had a similar question, this would be a hard topic to find with a title like that. 

I fixed it. At least it's tagged.

1 hour ago, Gene Howe said:

Thanks @p_toad. Didn't think of lubing it. I'm planning using 3/8-20 screws. Lube may be really helpful.

Threading a dowel is an idea that opens up more possibilities. 

I have done it a lot Gene, after all screws are used all the time. 3/8x20tpi ought to be fine. I have done mostly 1/4 X20tpi, and #12 24 tpi. never had one strip out in side ,edge,or end grain. It also depends on how often they are removed and retightened, or loosened and retightened. I use wax on the tap and also on the threads after the machine screw is threaded in. I do have better luck tapping the threads than forming them with the machine screw. If I use the screw to form the threads it sometimes strips the threads.

I have had mixed results with inserts. The brass ones after awhile want to unscrew with the bolt or threaded rod, and the barbed ones sometimes want to push out when inserting the bolt. both can be corrected with epoxy, but I hate that stuff.

Herb

3 hours ago, Gene Howe said:

I'm thinking of tapping some threads for machine screws in hardwood

 

When someone says "Machine Screws" I always think 12-24 screws and smaller.  Threaded inserts for 12-24 screws probably have threads similar to 3/8-20.

I've done very little of it, but with mixed results. Most of the dowels I threaded were Birch so maybe not hard enough or the threads not course enough???  Ironic you should ask this question today. I was perusing the interweb last night for insert sources and options to put threads in wood...might take a look at what Grainger offers to see if any of their products (Links below) might offer an alternative solution.

 

Both @Dadio, & @HandyDan make great points though. Herb noted we've been putting wood screws into wood forever and that works so...

Dan's point to using the inserts is the hole size has to be greatly enlarged for the insert. Looks like a 3/8" insert needs a 5/8" ID hole...most machine screw sizes appear to require a 3/8" ID hole; T-nuts, all smaller ID's required.

 

Great thread Gene...glad you asked...I'll be following close.!

 

https://www.grainger.com/category/thread-insert/fasteners/ecatalog/N-8nr

 

Grainger T-Nuts

 

 

 

 

Dave, Thanks for the link. But, in my experience, T Nuts are a PITA to install and end up with a smooth surface. I resorted to boring shallow recesses with Forstners. Then, installation requires a short rod and a hammer. I can't count the number of barbs I've bent. And, as Herb said, both the T Nuts and the threaded inserts tend to work their way out, absent any epoxy. 

For the project coming up, I will try the tap method. It's another mesquite slab. Pretty sure the threads will remain intact.  

It's going to be an end table to go with the river table. The leg system (another experiment) will require several bolts so that it can be flat packed.

Edited March 1, 20188 yr by Gene Howe

For that operation the 3/8 20 should work great. it will only be assembled and disassembled minimum times.  be sure to include a flat washer on the bolt head. Mesquite ought to tap nice and smooth too.

Herb

Gene if you thread wood the larger the thread the better. Fine threads kinda falls to pieces when taking off the die... And being something that small in diameter you wouldn't get much torque before pulling the threads off...

I think this will be an unhappy learning experience.. Thats what I am relating to you, an unhappy learning experience.. 

9 minutes ago, Smallpatch said:

Gene if you thread wood the larger the thread the better. Fine threads kinda falls to pieces when taking off the die... And being something that small in diameter you wouldn't get much torque before pulling the threads off...

I think this will be an unhappy learning experience.. Thats what I am relating to you, an unhappy learning experience.. 

Do you think a 3/8 bolt is too small? Is there a tap and corresponding screw/bolt that cuts deeper threads? 

 

Is a 3/8 bolt too small? Depends on how many and how deep you are going. If you used an M10-1.5 (just slightly larger in dia.) You would gain about 20% more material between each thread. The tread form is the same 60 degree. Whoever is doing the assembly has to know the limits of torqueing a bolt in wood. 

Here's my question, Gene.  Is there a reason you are using a fine threaded bolt.  A standard bolt is 3/8-16

How about some hanger bolts and nuts.  Thread the hanger bolts in when you get where you are going.