Threads cut in a walnut post

[4DThinker]

Right and left threads, 45 degree bit, Used the rounding gadget first to round a 1.5" square x 23.5" block into a 1.5" diameter cylinder.

For a small table idea I've got. The side cutting bit I ordered to cut inner threads to match is on the way. Hopefully I can cut matching threads that'll screw down/up on this post. A pseudo tensegrity project.

Closer look. Sanding them smooth shouldn't be too difficult.
4D

[4DThinker]

Rounded over the ends of the post. Wanted to use the moulding toolpath but it kept throwing an error no matter how I set it up. Ended up making a 3D model of the ball end and cut it as a 3D model.

Holes are where the screw went in through a hex block that was held in my 3-jaw chuck. I'll patch them when I find a 1/8" diameter walnut dowel section.
4D

[4DThinker]

Patched. Had to.

[Jimcad]

Looks great.
But . . . I hope you're going to take the tops off the threads or they'll bottom out in the internal threads.
Looking forward to the finished assembly.

Jim

[4DThinker]

Looks great.
But . . . I hope you're going to take the tops off the threads or they'll bottom out in the internal threads.
Looking forward to the finished assembly.
Jim

Thanks Jim,
The internal threads will be cut with a pointed side 45° V bit thread cutter. I won't have it to use until Monday at the soonest. This project is more about experimenting with the threading toolpath in Aspire to see if I can make threads that match the radial axis threads. If the tips need removing I'll chuck the post up in my lathe and handle that with a little sandpaper. There is an allowance variable in the threading toolpath to play with too. Hoping I can get the pitch set right and sneak up on a good match. The hubs/nuts won't be screwing up and down more than a few times. They are to tighten tension straps that will keep the post perpendicular to the base and the top when the post is twisted.
4D

[Jimcad]

Cheers Mr. 4D.
Show us the finished article please.

Jim

[4DThinker]

Thread cutting bit arrived. Did one test cut. Did thread down the post but was very loose. Reduced the diameter from 1.5" to 1.4" and redid the toolpaths. Good fit, threads down easily. Seems a bit crooked though as it goes down the post which is hard to wrap my head around.

Slots are for 1" webbing straps. Rounded over the approach edge on the slots with the moulding toolpath.
4D

[MiloScott]

Good fit, threads down easily. Seems a bit crooked though as it goes down the post which is hard to wrap my head around.

If the nut is held while the bolt is rotated. Does the nut "wobble", or is it at an angle to the bolt thread?

[4DThinker]

Good fit, threads down easily. Seems a bit crooked though as it goes down the post which is hard to wrap my head around.

If the nut is held while the bolt is rotated. Does the nut "wobble", or is it at an angle to the bolt thread?

Nut held in vise and post screws in without needing to wobble, but at an angle other than perpendicular to the nut.
I know the board I cut the nut from was laying flat on my CNC and the bit/Z travel was perpendicular to it. The profile cut around the nut is 90° to the face on all sides. I'm questioning the ramped spiral vector create by the threading toolpath. Pitch may have been off a little is all I can think of.

[MiloScott]

Nut held in vise and post screws in without needing to wobble, but at an angle other than perpendicular to the nut.
I know the board I cut the nut from was laying flat on my CNC and the bit/Z travel was perpendicular to it. The profile cut around the nut is 90° to the face on all sides. I'm questioning the ramped spiral vector create by the threading toolpath. Pitch may have been off a little is all I can think of.

I have cut many threads and never saw the threads skewed. How does it align if you flip the nut and use the other side to start. Same results? Did you verify the headstock center point and tailstock center point were aligned with each other when you cut the bolt threads?

[4DThinker]

Nut is the same no matter which side I screw it down on. My rotary axis chuck is perfectly aligned with the tailstock. In fact the original tailstock it came with was mis-manufactured and not aligned which I pointed out to Probotix. They offer a new one once they realized I was right. The post is the same diameter on both ends. It would have a slight taper if the tailstock wasn't aligned.

[MiloScott]

Nut is the same no matter which side I screw it down on. My rotary axis chuck is perfectly aligned with the tailstock. In fact the original tailstock it came with was mis-manufactured and not aligned which I pointed out to Probotix. They offer a new one once they realized I was right. The post is the same diameter on both ends. It would have a slight taper if the tailstock wasn't aligned.

I was just thinking of the tailstock misaligned. When I use a 1.25" surfacing bit to round the stock, cutting on top of the part, the tailstock could be off quite a bit and just shift under the bit surface. The vertical alignment between the headstock and tailstock would then control the taper rather than side to side alignment.

Other than mechanical alignment, I haven't experienced software issues while threading.

[4DThinker]

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.

There is some play between inner and outer threads. I suspect that inward ramp at the bottom left material that is pushing over/into the veritcal path so the nut has to tilt so the post can get past that section. A smaller start circle, and let the threading toolpath cut deeper to be out of the wood before moving in may be the solution.

[MiloScott]

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.
screw tread vector.jpg
There is some play between inner and outer threads. I suspect that inward ramp at the bottom left material that is pushing over/into the veritcal path so the nut has to tilt so the post can get past that section. A smaller start circle, and let the threading toolpath cut deeper to be out of the wood before moving in may be the solution.

I have noticed there is a difference if you start from the top or bottom of the hole, threading up or down, as to where it starts/ends. I pretty much always start at the bottom of the hole and thread to the top. For "nuts", I use a jig with a hole so the bit can extend past the bottom of the nut surface, ensuring a full thread at the bottom and top.

I also make the bolt first. I then cut the threads in the nut. Leaving the nut mounted, if I need to add a little more clearance I can recut the nut.

[4DThinker]

Hadn't noticed the Top to Bottom option. A quick check and it did produce a cleaner vector to start at the bottom. I'll give that a try tomorrow, starting with a 1" depth for a 3/4" thick board. Need to round up another scrap to use. I also cut the post first, so when I cut the threads I could leave them on the CNC to check fit. Both time though the threads were too big around rather than too tight.
I did a quick check of my CNC radial axis setup, and it looks like the rail that the tailstock rides on sags just a bit in the middle. So for anything around 2ft (of the 4ft bed length) the tailstock may be slightly lower. Roughly 1/64". A heavier block on the radial axis might even make it sag more. Short things or very long things with the tailstock near the ends of the rail there wouldn't be any noticeable alignment error. Indeed while they look the same one end of my 23.5" long post is at 1.4" diameter while the other is 1.385 checked with a digital caliper. Tailstock aligns with the chuck when brought up to it, but is 1/64" down relative to the Z axis/gantry near the middle of the rail.