Thread milling

[martin54]

slowoodworker

What problems are you having getting the two bits to close properly? What bits are you using to cut the threads? I still haven't looked at using slotting cutters to cut the threads so Ted would need to give more detail on that, I've now got a couple of bits for thread milling but have stuck with single form bits as these are more versatile than multi thread bits.

[kstrauss]

If you've figured a good way to get the lid and base to close tight I'd love to know.

Without being able to see your project (care to post?) I'm guessing that the problem is that your male threads do no go quite to the bottom of the lip on which they are cut. If so, the easy solution is to relieve the start of the female threads. That is, mill a groove from the top of the female part to perhaps 1/8-inch below the edge and to the depth of the crests of the male threads.

Apologies if this isn't what you meant.

[TReischl]

slowoodworker

What problems are you having getting the two bits to close properly? What bits are you using to cut the threads? I still haven't looked at using slotting cutters to cut the threads so Ted would need to give more detail on that, I've now got a couple of bits for thread milling but have stuck with single form bits as these are more versatile than multi thread bits.

As usual my fingers got ahead of my brain! I use the slot cutter to create the relief at the bottom of the threads, works like a champ.

[slowoodworker]

I understand that the slot cutter is for relieving the area at the bottom of the threads. But my slot cutters are 1-1/2" in diameter, plus I've never tried undercutting and that makes me a little nervous. (Nothing worse than miscalculating and coming in and slicing off the threads.) I think I'm using the same bit Martin is using -- and you have to clear a huge area for it to work. I think I have a fixture "designed" so I can hold round blanks before I do any further work such as pocketing, threading, and design on the top.
My first sample was in 3/4" pine. I think I'll have to go to 1" material for the "real" boxes just so I can get the threads deep enough -- especially on the top that has inside threads.
If I can get things to look/fit right I'll post plans and pics. These are xmas presents so you'd think I have lots of time.... We'll see

Rich Farwell

[martin54]

I've got a few bits but those boxes were made using the same bit that the vectric thread milling tutorial was done with. I wouldn't worry to much about any sort of undercut, I haven't tried it & all the boxes I have made to date are fine without one. If you are using the same bit that I am using then I might be able to email you a file to look at. You need to make sure the recess at the top of the internal threaded part is at least as long as the tool offset, can't remember what it is for that bit.
If your using the same bit then 3/4" stock might be a little on the thin side, depends on the pitch & how many threads you have, on the internal threaded part you need to allow for the tool offset at top & bottom of the threaded portion Plus the design on the lid is going to cut so far into the material as well
I haven't designed a jig to hold round blanks, I do all the box making using regular board, all I did was to make a jig with a male thread so I could screw the lids on & then cut what ever design

What diameter are you making them? What pitch are you using & how many threads are you cutting??

[TReischl]

My slotters are large too but I run them at about 16K RPM. I cannot get any slower than that.

The reason to undercut threads is to allow the lid to seat firmly and squarely when screwed down. The same thing can be done by relieving them on the lid side but that results in a thinner edge on the lid.

I am an old school programmer that started out writing g code by hand about a century ago, LOL. So it is no big deal for me to just hand code something like this. But I always do a single step line by line dry run to make sure I did not screw up a decimal place, etc.

The problem as I see it with the slotting cutters is that their size dictates how small the box can be. Digging around in machining stuff there are smaller diameter cutters but I do not do enough of this stuff to get me to buy one.

I use one of my vises to do this work. Just put in a couple of scrap wood jaws, bore them out and voila!

Right now I am reworking an end grain cutting board that did not work out as planned. Learned my lesson about inlays within inlays using the v carve technique.

[martin54]

Right now I am reworking an end grain cutting board that did not work out as planned. Learned my lesson about inlays within inlays using the v carve technique.

Ted, I think Rebecca bid an in the labs about inlays within inlays, might be worth having a look

[TReischl]

Thanks Martin! I will go have a look this evening.

[slowoodworker]

Thanks guys, you're giving me some good ideas to work on.
Martin, I gave some thought to screwing down the lid; I was afraid the lid might unscrew. But that might hold better than double stick tape or painters' tape and CA glue.
My boxes are 3-1/2" diameter; The bit is same as Beki's; pitch preset = uts5/8", pitch = 0.0909". The inside diameter for the thread is 3-1/8".
I got the fixture/jig cut out this afternoon -- very simple. If I can figure out how to download the image to this computer and how to upload my box file, I'll edit this post and add them.

I just upgraded to Aspire a couple of weeks ago from Vcarve Pro. There is so much to learn!
--Rich Farwell

[martin54]

Thanks guys, you're giving me some good ideas to work on.
Martin, I gave some thought to screwing down the lid; I was afraid the lid might unscrew. But that might hold better than double stick tape or painters' tape and CA glue.
My boxes are 3-1/2" diameter; The bit is same as Beki's; pitch preset = uts5/8", pitch = 0.0909". The inside diameter for the thread is 3-1/8".
I got the fixture/jig cut out this afternoon -- very simple. If I can figure out how to download the image to this computer and how to upload my box file, I'll edit this post and add them.

I just upgraded to Aspire a couple of weeks ago from Vcarve Pro. There is so much to learn!
--Rich Farwell

I don't think there will be any problems with the lids unscrewing but I haven't tried it yet If that does happen then I have some thin rubber that I could fit to the bottom of the jig for the lid to tighten down onto.
Something I do when I make all my jigs for the CNC is to put asymmetric dowel holes in them same as I do with double sided jobs. That way I know I won't have any problems putting the jig back on the CNC machine at some point in the future.
Those boxes in the post are 80mm so not to far off the size you have & I think the pitch was 2.5mm so that's also pretty close to what you have.

If you have been using vcarve pro then at least you don't have to learn from scratch Much of it is the same as I am sure you already know, best of luck with 3D modeling, it makes my head hurt My problems mainly start when I have a bunch of components that I want to join together, figuring out combine modes, base heights, fade & tilt etc etc to make things look right. Sure I will get there one day but like you say it's a lot to learn

[ElevationCreations]

My slotters are large too but I run them at about 16K RPM. I cannot get any slower than that.

Would a keyhole slot cutter work to perform the undercut on the threads?

[John Murphy]

HI Guys.
Here is a test piece I did a few years ago, using recently departed Paul Rowntree's thread cutting gadget, which I assume is very close to the newer Vectric Aspire version.

The major diametre is about 2-3/4" and a depth of 1-1/4" with a 3/16" pitch.
The material is 1-1/2" ranger premium MDF which yielded far better results than expected.

I used a set of boring bars for 60deg internal threading. Unfortunately they no longer sell the set, so I'm glad I picked them up when I did. I think I can thread up to 3" deep, I'd have to dig out tools and check to make sure.
The shank diametre is 8mm, which restricts those who only have the standard 1/4" or 1/2" collets. I run iso30 collet holders with er32 collects, so I can usually find a collet that will fit most any shank of cutter I want to use.

I have ground wing cutters with a 60deg angle tip, and these work as well, although you would obviously need a thread diamitre bigger than the threaded hole you want to cut.

Always remember to cut the male side first, so you can size the female on the machine. Learned from experience.

JOhn

[SteveNelson46]

My slotters are large too but I run them at about 16K RPM. I cannot get any slower than that.

Would a keyhole slot cutter work to perform the undercut on the threads?

Maybe, but the keyhole bit cuts a pocket at the bottom that's pretty deep.

[gkas]

Always remember to cut the male side first, so you can size the female on the machine. Learned from experience.

Good to know. It's like test fitting an inlay.

[kstrauss]

For the undercut you might want to consider using a keyseat cutter. They are available in a variety of diameters and cut widths. See https://www.amazon.com/Micro-100-KC-250 ... 00Q8MMO76/ for an example.