Mill Upgrades – Fixed Tool Changer 1

I’ve tested several tool finger designs for the fixed tool changer (eventually to be used on the rotary tool changer), and while I don’t have a final design yet I thought I’d share some data.

The goal here is to ensure retention while minimizing required force to grab the tool. These are PLA, but the production version will likely be Nylon. In the case of this fixed tool changer, the retention required is primarily going to be determined by the maximum speed of the table, which is 100 in/min. For the rotary tool changer, there may be higher accelerations, particularly at the end stops.

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Using a postal scale and slowly increasing pressure, I measured the force required to insert into the different designs. They are all the same basic geometry with some minor tweaks (except for #2, which is flat):

Design #1: 11 pounds. Tapered in both Y and Z  along the X-axis (which you can imagine as a line that splits the finger symmetrically).

Design #2: 12 pounds. 2D, flat sheet. Distorts significantly while trying to insert the tool holder.

Design #3: 15 pounds. Tapered only in the Y direction along the X-axis.

Design #4: 11 pounds. Added two additional bending locations and tapered in the Y direction, but this time the taper goes outwards instead of inwards.

Design #5: 21 pounds. This was my original design.

Now, some of you may be saying, “why didn’t you just simulate this and save yourself a lot of time?”. Let’s take a look at the results of a simulation on Design #4.Rev 4 tool holder body v4.png

This is showing the total deformation with 11 lbs of force applied. The force location might not be quite right, but that’s not critical here. Notice that maximum deformation is 0.005 mm — in other words, 5 microns. Now that amount of deformation is nowhere near the required deformation to seat the tool holder in the finger (approximately 4.25mm).

The first point of error in comparing these is the scale (and my measurements which are probably somewhat subjective). A better method for this would be using a setup where values could be pulled directly off the load cell, preferably with some tunable power source pushing the tool holder (like a pneumatic cylinder).

The other major factor is that these parts are 3D printed, so they deform more easily. Simulating 3D printed objects requires playing some funny games with things and is overall not that fun, so physical testing is easier and more straight forward.

Mill Upgrades – Air-Over-Hydraulic Drawbar Part 1

I spent some time reorganizing the shop after several weeks of pretty much total inattention to it. This included finally building a keyboard mount so I can now reach it while close enough to the mill to reach/look in (really handy when indicating stuff in). Not shown are the grinders and other welding supplies sitting in a large plastic bin and nagging me to come up with a real storage system on the wall.

I also made some real progress on the power drawbar. Most of the structure of the system is ready to go. I’m using an air-over-hydraulic system, with an Enerpac cylinder and a 33:1 pneumatic to hydraulic booster. Below you can see the system. The pneumatic valve is in place on the manifold, I still need to wire up the relay, and then I need to figure out the Mach3 side of things. I do think those parts will go quickly.

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I also have the materials for the new drawbar, but haven’t completed the new drawbar clamping nut, or figured out exactly how I’m going to setup the mechanical components to keep the Bellevilles centered on the drawbar and the drawbar centered in the spindle.

Not pictured is the two attempts at the mounting plate for the hydraulic cylinder assembly — the first was for fit testing and some critical dimensions were off just a little, the second I cut the wrong size stock and didn’t realize till a while into it. Hopefully attempt three will do the trick.

I also did some work to design a fixed ATC assembly I can use once the hydraulic drawbar is installed. This will be a good opportunity for me to test software as well, as I’m sticking with Mach3 for the time being (with the next stop most likely being LinuxCNC, although it’s possible I’ll go for Acorn Centroid). I’ve already started on a new screen set for Mach3 which includes an ATC, and expect that will be for sale at the same time the ATC is ready.

Fixed ATC Assy v4.png

Mill Upgrades – Flood Coolant Part 1

I’m trying to wrap up the documentation for the spindle belt upgrade so I can get it up on wcubed.co, and since spring has sprung I’m also pretty busy getting the yard in order. I did find some time to work on adding flood coolant and tying in the air blast delivery to it.

I’m using a Brute 20 gallon tank with some prospecting sifting screens, and the original 4 GPM coolant pump mounted on a polycarbonate stand to keep it above the coolant level. The manifold is from Automation Direct, and the hoses are standard Loc-Line (one 3/8″ NPT that came with the mill, the rest are 1/4″ NPT). The system is waiting on me to make a drain from the stand into the filters on the coolant tank.

I also have a new drag chain waiting to be installed, which is large enough to carry the coolant line. The Z-axis end stop sensor wire needs to be run down that, as well as the motor cable and the lines mist coolant and air blast, so it should help tidy things up a bit.

Bonus tip: when you have to tap some M3 holes but don’t have a tap holder small enough, a TTS ER20 holder can come in handy.

An easy guide to making a WooCommerce store

I’m mostly putting this up for my own benefit, as every time I end up doing this I have to relearn like 90% of the process and I’d like to have a reference document.

So, start by picking up a domain name. I like to use Namecheap, but there are a million domain registrars, pick your favorite.

Go download PuTTY if you don’t have it already.

Next, pop over to DigitalOcean. They have a great guide for setting up WordPress on one of their droplets (and a lot of other stuff): https://www.digitalocean.com/community/tutorials/how-to-use-the-wordpress-one-click-install-on-digitalocean. I generally start with the cheapest droplet and will move up from there if necessary.

When you get to the bottom of the page, there’s a section marked “Add your SSH keys”, which you want to do now because it will save you more confusion later. Open up PuTTYgen (which is a separate program from PuTTY, but was installed with it), and generate a key (you should be able to leave the default parameters, they should be RSA and 2048 bits). You will need to save the public key onto the server and keep the private key for logging in.

At some point in here, point the nameservers to the right place. DigitalOcean has a guide here: https://www.digitalocean.com/community/tutorials/an-introduction-to-digitalocean-dns but for Namecheap domains you can just go change the nameservers to “ns1.digitalocean.com”, “ns2…” and “ns3…”.

When you go to log in with PuTTY as shown later in the instructions, you need to use that key. They’ve also written a guide for that: https://www.digitalocean.com/community/tutorials/how-to-connect-to-your-droplet-with-ssh

Don’t forget to save the login settings in PuTTY.

While you’re SSHed into the server, follow these instructions to setup an SSL certificate on your server: https://www.digitalocean.com/community/tutorials/how-to-secure-apache-with-let-s-encrypt-on-ubuntu-16-04

Now your server should be running WordPress and you should have a valid SSL certificate. Go make a login for your site. Note: do not use “admin” — this is a potential attack vector; I strongly suggest using a password vault in general in your life, and in particular using a random character name and password for the site. Remember that anyone who has this login has access to all the data on the site, including the database.

Go to settings, and change the “WordPress address” and “Site address” to the url you got the SSL certificate for. Note that it must much exactly — if you got “xyz.com” you should put in “https://xyz.com”, not “https://www.xyz.com”.

The next step is to add plugins. I am not a guru of WP plugins by any means, but I like:

  • Obviously, WooCommerce. Without this, it’s not a WooCommerce site.
    • WooCommerce Services — supports other plugins.
    • WooCommerce PDF Invoices and Packing Slips
    • WooCommerce Stripe Gateway
    • WooCommerce PayPal Express Checkout Gateway
    • UPS (BASIC) WooCommerce shipping
  • Really Simple SSL
  • Jetpack by WordPress.com
  • Backup WordPress
  • All In One SEO Pack

You’re ready to go — setup products, fine tune your marketing, make whatever custom pages you want.

Mill Upgrades – Spindle Upgrade Part 4

Time to switch the tapered roller bearings (TRB) out for angular contact bearings. The primary benefit is that AC bearings allow higher speeds, particularly when running only with grease. First step was to pull off the seal above the top spindle bearing, remove the nut and pull the spindle out.

I dunno what kinda grease was in here, but there’s certainly a lot of dirt, probably largely as a result of having too much grease. This machine has probably only run for a couple hundred hours, so realistically the grease pack it had now should have lasted a while, and you can see in the first picture that the rollers look pretty clear (the grease forms a thin film on the rotating elements of the bearing).

I didn’t take any pictures apparently, but to get the quill out of the machine, you need to remove the quill retaining bolt (on the left side of the head), then loosen the quill lock. If you have the quill arm that may need to be removed, but as I have already removed mine I’m not sure. I have also already removed the quill DRO and the clamp that holes it

The next step is to knock the TRB cones out of the quill.

I cleaned up the quill face a bit after this, but you can see how much grease was jammed into the rollers and cages when I removed them, and how dirty the inner bore is. Most of the inner bore was hard enough it didn’t come off by wiping, and that stuff I left in there. Whether that was a good choice remains to be seen.

Time to press in the new AC bearings. Note: it would have been a better plan to grease them before doing this.

And back into the machine.

Now, I put way more grease than necessary because I forgot to grease them before, and my hope was that some excess would move under gravity in the top bearing, and that I would force some through by hand in the bottom bearing. I also wiped away a lot of the grease after running the spindle at 500 RPM for a little while to warm things up and spread the grease onto the balls. You’re only supposed to fill about 1/3 of the open space in the bearing (according to SKF, who should know), however ultimately the grease will convert to a thin film and coat the bearing, and any real excess will be forced out, particularly at high RPM. Excess grease will hold onto dirt and potentially migrate back into the bearing which isn’t great. If the space confines the grease in the bearing it will also cause excess heating, even if it’s clean.

Here’s what they look like after a few hours of running. I ran the spindle up to 7k in 500 RPM increments over the course of 5-6 hours (I was working on other stuff around the shop, the only rule I had was that I waited at least 10 minutes to measure temperature, and if I had already measured noise then I confirmed the measurement).

Spindle bearing noise comparison.png

The noise produced with the AC bearings is lower than the TRBs, although the modified motor and spindle pulley mounting may be a factor in that. Both are way better than the geared setup, which ran at 85 dB at 3k RPM.

One interesting thing to note was the peak around 6k RPM — some sort of resonance frequency perhaps. I remeasured that point going up and down several times to confirm, but it really does get quieter if regardless of whether the RPM is reduced or increased from there.

Spindle bearing temperature

Both bearings are in a good temperature range for the application, and there’s certainly head room to run the spindle faster. I’ve gotta scratch my head some more about why the smaller bearing is hotter.

Time to pop the seals back on and try out ripping some aluminum.

 

 

Mill Upgrades – Spindle Motor Part 3

The new spindle motor and pulleys are finally installed and working (and all the gearing and oil is out of the head).

As you can see in the picture below, I ended up with two cap screws to hold the spindle pulley in place. This is because I did a poor job on the bore and the pulley had 0.020″ runout. I just added the second cap screw and got it to within 0.002″, which really reduced the noise level.

The next step is to run the spindle up in steps and see how the temps look. It’s currently running the stock bearings, but I do have replacement angular contact bearings that are good up to at least 8k RPM with grease.

After that I want to try out some commercially available pulleys as I put together the BOM and instructions for the plans I’ll be selling.

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The biggest benefit by far is the difference in noise level. It now makes 77 dB at 3k RPM, compared to 85 dB with the gears in place.

Mill Upgrades – Enclosure

The picture above is my mill, a Precision Matthews PM940CNC (940 is the table size – 40″ long, 9″ wide). I got one of Matt’s first batch in 2015 (it has now been completely disassembled twice, first to move into a basement, then to move into the garage of my new house). I paid $7,200 for it, so I think there’s some good value in it (Tormach’s most similar model, the PCNC1100, starts at $8,400). It has a cutting volume of 3.5 cubic feet (X-23″ ,Y-14″, Z-19″), which is a little bit more than twice the PCNC1100’s, although a lot of that is in Z and is often not useful. It has a 1.5HP geared spindle motor and is setup to run at 3,000 RPM max from the factory. The axes motors are steppers, running double nut ballscrews. The machine itself weighs about 900 pounds (not including the control box or the stand).

The downside of this machine is that there is no upgrade support. Tormach offers an enclosure, a power drawbar, an automatic tool changer, etc. The PM machines come with an automatic oiler setup (except on the Z-axis), but other than that you’re on your own.

The first thing I wanted to add was an enclosure, because this thing can move a fairly large amount of aluminum in short order, and for cuts that require coolant, it really helps to keep it contained.

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The enclosure is made with a 1/8″ carbon steel drain pan, 1″ square T-slot aluminum extrusions, and 1/4″ thick polycarbonate. You can purchase the plans on my site.