Threaded post, radial cut

[4DThinker]

This will be the center post of a small table project idea I have.  Left and right threads, 45 degrees, walnut, on my radial axis.

 

 

I've ordered a side cutting V bit that hopefully will cut the inner threads of the nuts.  I'll post the final project if it actually works out.  

Took some brain scraping thoughts to get the toolpaths made.  Used the rounding gadget in Aspire to turn a 1.5" square block into a .15"d cylinder. Had to play with the feed speed to get a good spiraling cut with the V-bit.  Some harmonic vibration as the bit got closer to the center which I dampened with my hand under it as it slowly spun.  

4D

[4DThinker]

Rounded over the ends of the posts.  Wanted to use the moulding toolpath but no matter how I set it up it threw an error.  So I modeled the ball end and cut it as a 3D model.

Holes are where the screws went into it through a hex block that was held in the 3 jaw chuck.  Other end has a center hole where the tailstock center held the end. If I can find a 1/8" diameter section of walnut dowel I'll patch the holes.  They aren't critical to the design and wouldn't be seen, but I'll know they are there and that'll bother me a bit until I'm finally forget about them. 

4D

[Grandpadave52]

Interesting project. Will definitely be following along.

[4DThinker]

I could not find anywhere on the web that would sell me 1/8" diameter wood dowels.  Looking through a cheap plug cutting set I have I found one that claimed to be for 1/4" plugs but in use it made plugs closer to 7/32".  Made a few in the end grain of a walnut scrap, then found a drill bit that would make a snug hole for them.  Drilled out the screw holes and plugged them up. 

The ball ends will rest in ball socket cut in the bottom of the table top and top of the X frame base.  Thinking about setting in some HDPE to cut the sockets out of. 

4D

[4DThinker]

Thread cutting bit finally showed up.

Glad I did a test cut.  First try in scrap threaded down the post but was very loose.  I reduce the diameter of the vector used and tried again,  This hub nut threads down easily with good but not too tight fit.  Slots in the hub are for 1" wide webbing straps. I rounded over the approach edge for the straps with the moulding toolpath in Aspire. 

4D

[DuckSoup]

  Okay you got my brain going, are you going to use this for a project or is this a test piece?

[4DThinker]

It is a project if I can figure it out.  Never used the threading toolpath before.  A close look down the inner threads of the nut show even vertical threads on one side, but as you spin to the other side they aren't aligned. I notice the threading toolpath does a spiral ramp from the center out to the edge, then a ring around as if to chamfer the edge before starting to ramp around to cut the threads. At the bottom it pulls in as it is moving down before moving to the center to move up and out. 

I think my starting circle is still a little too large as there is some play between nut and post.  The section at the bottom that pulls in is what is uncut and pushes the post over.  That accounts for the tilt.  I'll revise the starting circle smaller, recalculate, and make a new test.  This time I'll lie and have it cut threads deeper hoping to get past the wood before pulling in.  I have an open area under where the hole is cut to allow that. 

[DuckSoup]

So, when you turn the "bolt" right or left the nuts will travel either towards each other or apart, right?

[4DThinker]

2 minutes ago, DuckSoup said:

So, when you turn the "bolt" right or left the nuts will travel either towards each other or apart, right?

That's the idea.  Post trapped between sockets in the top and the base.  Tension straps down to one nut and another set up to the other nut.  Twist the post to draw them both tight.   This presumes they'll both get tight at the same time, meaning they have to be carefully made, all the same length to a nut.  I've pondered splitting the post then putting it back together with an axle and thrust bearing between so each half can be turned independently.  

[JWD]

I wish I'd seen this earlier.  Making dowels is easy.

 

This sounds like a really cool project, looking forward to seeing it progress! 

[4DThinker]

3 minutes ago, JWD said:

I wish I'd seen this earlier.  Making dowels is easy.

True.  It was the 1/8" diameter that set me back for a few minutes at least. 

I'm  also looking forward to see progress on it.  I keep bumping in to roadblocks though. Got to get cutting threads that don't make a wonky nut all figured out before moving on. 

[JWD]

3 minutes ago, 4DThinker said:

True.  It was the 1/8" diameter that set me back for a few minutes at least. 

I'm  also looking forward to see progress on it.  I keep bumping in to roadblocks though. Got to get cutting threads that don't make a wonky nut all figured out before moving on. 

 

The trick is to use a very thin dowel plate - I use a piece of 10 gauge scrap (mild steel is fine) and relieve the back side of the holes with a countersink bit.  This is a rare case where the vibrations from a fluted countersink are good since a bit of corrugation to the hole is fine.  Make a series of holes decreasing in size, and start with a square blank chucked in a drill.  Run the blank in and out while spinning, angling relative to the hole you're using to reduce the diameter of the dowel relative to that of the hole (this is why the plate needs to be thin).  More angle gets you a smaller dowel until it starts to corkscrew, then you go down a hole size.

 

It makes a kinda ugly dowel, but for most dowel purposes you don't care if it's on the rough side.  I've never made them 1/8", but I've done lots and lots of 3/16" ones this way - never even looked for dowels to purchase that small, just made them out of what I had around that was either a good contrast or a good match for what I was doing.  Nothing about the method is particularly calibrated, a lot of trial and error if you're looking for precision, but wood has so much spring that you can get away without a ton of precision.

 

I can't imagine cutting the inside threads, I'm far too stuck in metal tapping methods to make sense of it without seeing it done.  Even in metal I have the impression that thread boring is not easy, the few times I've run across stuff done that way we've had to clean them up with a tap - I know it's done routinely and effectively, just never seen it myself because everything I see at work is a one off, and rarely do they have an expert CNC machinist, usually its an engineer or grad student who thinks they are a machinist.

[4DThinker]

Well,  Third time is the trick.  Had to set the depth of the threading toolpath 1/4" deeper and pray that the bit wouldn't slip out of the chuck.  Now I need another scrap to make a good hub nut with RH threads out of. 

I know that dowel making through a metal plate trick, but finding a thin plate of metal is a challenge in my woodworking tool shop areas. My shop teacher way back in 1977ish showed us. That was when there was no place around and no web source to check for unique sized dowels from assorted hardwoods. 

4D

[JWD]

I don't know how widely known that particular method is, so I usually assume most woodworkers think the only way is to use a commercially made heavy plate like LN's and are stuck with their calibrated holes for calibrated dowels.  Sounds like you had a much better shop teacher than mine, he had no idea how to make dowels or do a lot of stuff that later amazed me when I learned it in working shops.

 

Most of the plates I've used were nothing more than hot rolled flat strap from the hardware store.  I think I made one out a scrap of O1 and never bothered hardening it.  Its so quick and easy to do with a drill press that I don't bother worrying about longevity of the steel.

 

I'm curious how many passes get made threading your nut?

[4DThinker]

5 hours ago, JWD said:

 

3 minutes ago, JWD said:

I'm curious how many passes get made threading your nut?

Center area pocketed out with a 3/16" spiral upcut end mill.  Threading then done with side cutting V bit down (or up) a single spiraling vector made by an option on the toolpath menu of my CNC software (Aspire from vectric.com). 

In use the hub nuts are just to snug up flat webbing straps to stabilize the table structure. Spin them down (or up) close to where the straps can be easily attached, then twist the post to tighten them.  I'm hoping that the tension won't just un-spin the post until relaxed and that the mechanical advantage of screw threads will win out.  If that happens I have an idea on how to keep the post from twisting once set. 

[JWD]

56 minutes ago, 4DThinker said:

If that happens I have an idea on how to keep the post from twisting once set. 

Pipe dope

 

Or pine tar!    I love pine tar for some weird reason, always looking for uses.

[4DThinker]

I had more of a mechanical idea in mind, but if that doesn't work then pipe dope it is!  As there is no pine in the design I'd need walnut or red oak tar. 

4D

[JWD]

59 minutes ago, 4DThinker said:

Center area pocketed out with a 3/16" spiral upcut end mill.  Threading then done with side cutting V bit down (or up) a single spiraling vector made by an option on the toolpath menu of my CNC software (Aspire from vectric.com). 

 

What the bit looks like just clicked  I had my head stuck on single point threading, which made little sense in wood.  That bit sounds much more sensible... coffee took longer than usual I guess, or Grandpadave ate all the donuts and I'm operating on a deficiency of sugar  

 

Does your model account for the projection of the bit profile given the thread lead?

[4DThinker]

4 minutes ago, JWD said:

Does your model account for the projection of the bit profile given the thread lead?

I'll assume all account was taken care of as I now have a nut cut with the bit that spins nicely down the post threads cut with a more typical V-bit on my rotary axis. 

For this project the lessons I learned in the drafting class I took in high school have been useful.  Started with a section view of the V-bit down in my post, measured the depth and width, then compared them with the specs of the side cutting V bit before I bought it.  Knew it should work if I could just set up the threading toolpath details correctly.  Not obvious what every option meant but after 2 failed tries I got one nut that fit nicely. 

[4DThinker]

Test done for strap attachments to the hub. 

#9 drill bit made a snug but slip fit hole for the 5mm pins. There is a grommet in the ends of the straps.  When the straps  are under tension they'll make sure the pins can't slip out.  Friction of the fit in the hole also keeps them in place.