Threading wood to replace inserts

[21incher]

I have a project that I want to thread the wood instead of using inserts. I tried metal taps but couldn't get nice threads in wood without imperfections.  I just want to make the parts with the cnc and avoid buying and installing 200 inserts. I looked around and found taps made for wood and finally ordered a set from Infinity tool. I was surprised how they just came in plastic  sleeves and looking at them there  is no country of origin stamped on them. They were expensive but look like Chinese taps made from Chinesium so I have my doubts about longevity.  Tried them all and the results are excellent with perfect  threads and no tearouts like the metal taps. The threads seem very strong in ash and are very quick to make just using a drill. Thinking about trying wood wax on the bits to make them last longer like my Beall taps. Hardwood and softwood require different pilot holes but I didn't  have any softwood to try. Thought I would start a thread where we can share experience trying to use wood threads instead of inserts to see what works. Here's what they look like


 

 


 

These are the Beall taps I have had success with using threaded wood bolts


 
I guess the knobs with threaded studs will require a good coat of protectant to keep the steel threads from rusting with moisture in the wood.

[Old Greenhorn]

Well I have never thought of machine threads in wood having much strength. I am wondering what your application is for all those holes? Moisture changes and all that wreak havoc with machine threads in wood.
I have one regular product where I tap a machine thread into wood for an 8-32 thread, but this screw is used more as a locking pin than it is a screw and the thread is just to hold the pin in it's place. There is no pull force on the screw at all. It is finger threaded in and out and does not need to be tight.
SO what do you have going on there?

[doc henderson]

could reinforce with thin viscosity epoxy, and then retap to stabilize and strengthen.

[21incher]

I'm just making a bunch of adjustable racks and some holding fixtures first to see how they work. Mostly 3/4 thick indoors use. I tried stripping out the 3/8 thread with a wrench and washer under the bolt head but it didn't cranking on it with about a 6 inch long wrench. The 3/8 and up seem very strong. The 1/4 and 5/16 will take all the torque I can put on them with a screwdriver without  stripping  in 3/4 ash. I'm going to try some inch thick maple next. Had to order some sharp brad point bits first because mine have all seen 30 years of use and I can't  figure  out how to resharpen them plus ordered a set in 1/64 increments to see how hole size affects thread strength because their recommended sizes don't seem prefect. The bolts go in and out easily with no shake and no apparent wear. I am going  to try the Porter cable screw wax lube I use on the Beall threads to try and prevent rust. Just an experiment for me that I have no idea how it will end and wondering if someone else has already had success or failure trying something similar

[21incher]

could reinforce with thin viscosity epoxy, and then retap to stabilize and strengthen.

I was thinking super glue may be another option. Could apply it with a microfiber qtip in a drill but that's just extra  work  if not really needed.

[Old Greenhorn]

If it were a few years ago I could give you the strip forces for various screw threads off the top of my head, but that stuff has faded away, there are tables out there though. Usually I figured 3 full turns (threads) on a given screw size gave you the best you could expect for that screw. Now in any hardwood, I would imagine increasing that number of threads would reduce the tearout force per thread.
I suppose for your project and the stated 'playing and learning' it will be interesting to see what you learn. For me, I just prefer using inserts when I need to use machine screws. I do prefer using machine screws over woodscrews for anything that will have to come apart and go back together during it's life, like the removal of a heavy top from heavy legs for moving.
I recently bought a bulk bag of inserts from McMaster for a reasonable price that makes it easy to use them. They have quite a variety available.

[doc henderson]

I think in wood there will be some variability depending on species and grain orientation.

[21incher]

I guess the way I see it is inserts rely on threads in wood for pull out strength so just going with a slightly larger and longer bolt thread should be equivalent.  Now you have me thinking maybe I should pickup a digital  torque wrench to get some strip out torque numbers in different woods and grain at different numbers of tightening to see if that diminishes the value by much. The seasonal movement  of the mating member  will be constant weather threads or inserts that may require some type of spring washer.  Would be fun to do a comparison but I think I will try winging it first.
.

[Larry]

I tap many different threads using standard metal taps.  After I tap the hole I squirt thin ca glue into the threads, hit with accelerator, and run the tap in a second time.  The species of wood does make a difference but walnut, maple, and cherry seldom presents a problem.

I make lots of lamps.  This style gets three 10-32 set screws to hold the globe in place.



This style gets one 1/4-20 screw to hold the globe on.






Granted the screws only get used when its time to change the light bulb which doesn't happen often.



This is a shop made vacuum chuck for my wood lathe.  It's 1-1/4 - 8  and gets installed and removed probably 6 times a week.  It has been in use for 4 years without problem.

I also chase threads on the wood lathe for small boxes, and cremation urns.  They also get the thin ca trick on the final pass.  Wood species does make a big difference when chasing threads.

I also use lots of inserts, but not because they are better.  In some places a insert looks more professional than just tapping the wood.

[21incher]

Thanks Larry. I will have to pickup some of the thin super glue to try. I use the gel version now and that doesn't  soak in at all. I tried some of my larger metal taps but the chips didn't clear good and damaged the threads especially  when backing out. Guess I will try a 10-24 and see how the small ones work because these only go down to 1/4.
great idea with the glass globes. I have about 20 of them that were in the house when we bought it I replaced and was trying to figure out a way to use them. I'm going to steal your idea for the simple base. May try some cherry cookies I have that are dry also.

[Crusarius]

It is surprising how some materials hold threads well. For my dogtag fixture on my CNC I used 3/4" MDF and I just ran a 10-24x1/2 screw into the MDF. So far it has been holding up great using an M12 impact driver to tighten and loosen the screws.

Here is the full fixture. all those holes were threaded by running a 10-24 into screw into the hole.


 

Closeup


 

and just for an explanation, those blue pieces I 3d printed they are oval pieces that have a relief underneath. I place the dogtag into the pocket the turn those till they sit tight against the tag and tighten the screw. The pockets were machines using a dovetail cutter so there is a nice undercut that holds the tags from lifting on all 4 sides. The fixture is setup to handle business cards and dog tags.

[21incher]

Bits came today and tried the 3/8 and 1/4 threads with accurate holes. Grabbed some 1 inch walnut.  Drilled holes, countersink both sides and then threaded. Perfect threads in the walnut.  Grabbed  a 3/8 SHCS with some washers and tried to strip the bolt out with a standard 5/16 hex wrench.  Could not and the washer sunk some in the walnut before  I couldn't turn it anymore.  Surprised me as I thought the walnut would strip out easily.  Put them in and tightened then out 6 times with no damage to the threads.  Same with the 1/4 didn't strip after several tightening as tight as I could get them with a std 7/16 wrench. I was afraid to go any tighter with the 1/4 bolts because  they are only grade 2 and the heads snap off easily.  Now I know they will work  for my needs.


 

 

 

 

 

 

 

[Crusarius]

That will work. can you try a piece of pine?

[21incher]

That will work. can you try a piece of pine?

I don't  think I have any pine. I'll dig out a piece of cottonwood that seems even softer then pine.

[21incher]

Had some 7/8 cottonwood and used the 3/8 tap. Drilled 2 of the hardwood size pilot holes  and 2 of the softwood size pilot holes. Threads are not as clean and sharp as harder wood. The 3/8 SHCS bolt stripped out the hardwood size taps with a good tightening. The softwood size  holes also stripped out but it took twice as much force  as the first set. I bet at an inch thick wood would hold them pretty good but I think an impact driver will strip them in any type of wood if you're not careful.


 

 

[Larry]

One learns so much from testing, I'm glad to see your results.  About the same as what I have experienced. 

[doc henderson]

I ordered the 9 pcs master set with 6 SAE and 3 metric.

[21incher]

I almost got the full set but metric hardware is quite pricey so just got the ( 6 ) inch size for now.  They do work nice in hardwood. Just like tapping metal a little  countersink on both sides of the hole makes for clean threads with the tap easier to start.  Sorry  for being a bad influence but they do work  nice.

[Crusarius]

Thanks 21, thats really helpful.

[21incher]

My wife wants a little  bench for by the door.  I grabbed a walnut  cutoff and flattened it with my flattner then planed it and started hacking the ends to go with the live edge. Decided  that I will blind tap the board and bolt  legs in place to see if the threads will hold up. Funny  thing is I think that Amazon thing is listening to us because I went to Amazon and a pair of clearance Chinesium bench legs popped up for $18 so I just bought  them and don't have to make my own. Won't be here for a week though.  I played with 1/4 blind taps to mount them in scrap that look like they will work.  Busted one open and the threads  don't look bad. Impact driver works on #1 but #2 strips them right out  at 3/4 inch depth. Put a drop of super glue in the threads before inserting the bolt and it's  permanent.  Need to find some  kind of applicator like a uhmw bolt that the glue won't  stick to. I'm going to try the bench first and see if they can stand up to my fat butt.  ;D


 

 

 

[21incher]

Just finished up a small bench for my wife made from a walnut cutoff and clearance legs from Amazon.  Got. 2 sets for 18 bucks.
(28) 1/4-20 SHCS give it a real primitive industrial look. My under $10 bench that will probably last forever and my wife is happy. Next to dig out a big walnut slab for the second set of legs.

 

 

 
A quick couple hour project with no frustration or complexity to end the year.

[Crusarius]

subtle and beautiful. I really like those legs.

[doc henderson]

21 what did you use to make the large radius round over on the ends?

[21incher]

subtle and beautiful. I really like those legs.

I was surprised to get 2 sets because I thought it was 2 legs or one set.  They are nice but the ground area where they are welded shows unevenness in the paint. Going to repaint them with hammer tone paint when it warms to hide that. I think that Amazon thing listens to us because I was talking about buying some cheap legs and all of a sudden this deal popped up 

21 what did you use to make the large radius round over on the ends?

I started with power plane then went to a spokeshave followed by the Shinto file and then sandpaper. Tried to make it vary some to go with the natural edge. I just bought a 3d CAM package that I am going to try and work out a more natural looking random one that I can do on the cnc router in the future.

[doc henderson]

can you provide a link to the legs?