My build has finally begun and in this post I will take you on the building journey.

The machine frame

My machine frame is built out of 120x120x4mm thick steel tubing. I chose this size as I could get it relatively cheaply. It is massive overkill, however. As my shed only has a small door it needed to be able to come apart easily so I opted for various bolted connections instead of welding it fully (which would have been much and much easier).

I added some extra supports for the machine bed which is not shown in the image above.

For painting I opted for Nelfamar Vinyl Plus which as a marine grade vinyl paint. I used this is various outside based projects before and it is easy to use, durable and quite affordable. The color I opted for is RAL3002 “Kern red”.

Concrete time

I wanted to take advantage of the vibration dampening properties of filling the machine frame with polymer concrete such as UHPC or Durfill. I describe the workings of that in this post here.

As Durfill is relatively expensive when you use it in low quantities I opted for using off-the-shelf pre-mixed concrete from the local Hornbach which at 2.75 EUR per 25kg bag is a steal. I added Moertelshop’s Flup4 to it to enhance its properties.

To cover the bolts I added grease to them and tighten them to the steel base. After semi-drying the concrete they were removed. I still need to do one of the steel legs. When I have some time in the coming weeks I’ll proceed with it.

Aluminium extrusion

For the machine itself, I used 80x80mm aluminum extrusion for the Y axis and 120x120mm extrusion for the X axis. The gantry risers are also 120x120mm aluminum t-slot profile.

Again to enhance it’s stiffness and vibration dampening properties I have filled these with UHPC polymer concrete. The specific product I used is Durfill by Durcrete.

It performs better than regular concrete or run-of-the-mill UHPC. As the volume for these aluminum extrusions is limited I chose the more expensive but better-performing Durfill product.

Polymer concrete time – Durfill

Durfill expands a little to ensure a good hold on the containing material. To ensure a clean mounting surface a spacer was created to prevent it from expanding past the edge.

Afterwards the spacer can just be washed out by washing it out with water. This method is extremely simple but works well.

With the Durfill, I just followed the mixing instructions and poured it into the aluminum extrusion. Whatever was spilled on the side, just wash it off with the garden hose.

After drying, the washed out spacers of the riser tubes look like this:

I did some video recording during this process. I’ll be uploading that somewhere in the coming weeks on my youtube channel.

The gantry tubes etc have also dried at this point.The weight of the table frame is about 400kg after filling it with concrete and mounting it togther.

Mounting and adjusting the Linear guides

For my design I utilized Sorotec Blue‘s HGR20 rails with P – precision class and P1 preload.

One of the first things I had to do was to create an adapter in order to allow two HGW20CC carriages and my dial indicator to be mounted to it. With a hole in the middle to tighten the t-slot nut and bolt. If you are interested in the drawing of this just hit me up on Discord.

After finishing this on my HBM BF25 mill (glorified drill press) I mounted it on my Y axis rail.

Buy these t-slot nuts!

I used the regular “twist and turn” t-slot nuts before and they are… very bad for this application. After switching to the model on the right all my adjustment issues went away. I was able to align the whole rail in just a few minutes instead of an hour of tinkering. Do not cheap out on your (t-slot) nuts!

Get it here

After using the premium of style of t-nuts the adjustment went swiftly.

Video of the linear alignment

I aligned the distance between the blocks to about 10um. This took about 15 minutes of work. Good enough for me

Conclusion – Mightymill build Part #1

I was able to make a good amount of progress so far. The next step is starting with the Z-axis and getting that going. Make sure to subscribe to the newsletter to make sure you don’t miss any updates.

Feel free to reach out to me on discord

Continue reading

Read my findings here…

Also featured on Hackaday

Introduction – My cheap Lusintun ATC cnc spindle

Several months ago I was looking for a spindle for my up and coming CNC machine. I had been drooling at a cheap BT30 ATC cnc spindle for a while. And I decided that it was finally time to take the plunge. I found a few options on Aliexpress, but they were all quite expensive. So I kept looking and eventually found a cheap atc spindle that was in my price range. Initially I was planning using it on my DIY PrintNC metal cnc router build but later on I decided to proceed with my own design.

Lusintun BT30 3.5Kw 8 pole 18000RPM CNC spindle

It is quite nerve wracking buying a 1000$ atc cnc spindle which to you is unproven and especially on Aliexpress… But I took the gamble.

4 pole vs 8 pole motor?

Which one is the best to buy?

I made a graph of the torque vs RPM for the 4 pole and 8 pole equivalent. This is based of the information provided by Lusintun :

Based on my usage alu / plastics / steel milling the 8 pole was more fitting. For reference a regular 2 pole 80mm spindle has 0.68Nm peak torque at ~18000 rpm.

Inspecting the cheap ATC spindle motor

The spindle arrived a few weeks later and I have to say that I am very impressed! It was very well packed. I have never had anything from aliexpress come in such well prepared and professional packaging. Unpacking it and inspection the spindle itself it seems very well made.

Initial issues

Here it comes …

The VFD was set up directly from the factory so it was plug and play. The issues that I was relating to the NBT30 tool holders that were provided by the sellers. Everytime I ran them above 8000-10000 RPM on my atc spindle I felt and heard serious vibrations coming from the the tool into the machine SHIT!. It was time to investigate.

Runout measurements

To make sure the issue was not related to the spindle having excessive runout I purchased a Mitutoyo 2um dial / test indicator to verify the suppliers specification of <0.001mm runout of the spindle cone.

The needle basically did not move. The spindle met the <0.001mm runout specification with ease.

Vibration measurements

After contacting the seller on Aliexpress they assisted me well in measuring and validating that the spindle is not the issue.

In order to measure this properly I needed some extra gear. There comes the SNDWAY handheld SW-65A vibration meter:

SNDWAY Handheld vibration meter SW-65A

Tool holder vibration range: 0.4-2.4 mm/s – spead = 6x
ER32 nut vibration range: 0.2-4.0 mm/s – spread = 20x

Motor vibration vibration measurement has good results. The motor is good, the holders are the culprit.

Findings

Tools are not very good. Target for a decent cnc setup is <1mm/s of vibration for the whole setup (toolholder + nut + tool).

The ER32 nuts of these tool holders were especially out of spec.

As a result of this the Aliexpress seller gave me a refund for the toolholders and I bought an alternative that worked well for me:

ISO 30 ER 32 UM 45L tool holder – Balanced 30000RPM *need to buy separate BT30 pull stud*

With this holder my vibration measurement was <= 1mm/s so fit for purpose.