Category Archives: Hobbymat BFE65 mill

Mill table DROs and way covers

March 2015

Counting turns of a handwheel is error-prone, inefficient and… dull. Wanting more spark in my life I decided to add DROs to the mill table.

I also installed some way covers at the same time as the scales – to prevent chips from collecting on the ways and also to protect the scales.

I have been using the DRO almost daily for a year and a half, and wonder how I ever managed without them.

Capacitive digital scales (abandonded)

I originally planned to use cheap(er) capacitive scales like the ones below, and build an Arduino-based display head. However, after MUCH sodding about and cursing I abandonded the capacitive scale approach and bought a DRO kit off eBay. For the gory detail of my attempts to build an Arduino-based reader see this page.

I did have a much more detailed write-up of installing the capacitive scales, however I had to switch to a DRO kit off eBay so this is a much shorter write-up.

ScalesDumped in the ‘too hard’ basket – I could not get a consistent reading from the heads.

DRO kit off eBay

I bought my kit from seller motor-mall. It arrived from China in just a week. The kit contained the multi-function display, and three linear scales.

There are many sellers offering the same or similar kits. Mine is made by ShenZhen HengXingXing Precision Instrument Co Ltd, and is the GCS series (GCS-900-3DB). Total cost in early 2016 was £250.

The display head comes with a number of functions. However, I only ever use the “1/2” function. I would probably use more but the English in the user manual is indecipherable. “Align the Goddess with the making part.” is a typical example. (I did my best with Mrs Naut as the Goddess but found that she is not adjustable.)

I paid a little extra and went for the version with 0.001mm resolution (instead of the standard 0.01mm). Not that I think I can machine to this level of accuracy, but to be able to detect slight changes – in the same way that the needle on an analogue dial may move around inside the dial’s smallest divisions. I am glad I went for the higher-resolution version, as I can now know when the gibs are loose, and get early warning of when things are not going to plan.

The head came with a variety of bracketry which made mounting it a doddle.

The only gripe I have is that the Y-axis in the head stopped working after about a month. I just disconnected the lead to the linear scale, and plugged it into the X-axis port on the back of the head. I did not follow this up with the seller…

The scales had solid mounting holes, and featured a yellow strip that neatly opened and closed around the link to the reading head. The heads have a mm or so of play in them perpendicular to travel, which made installing them easy.

X-axis

I decided to place the X-axis scales behind the table, out of the way of the gib adjusting screws and X-axis stops.

I installed the scale upside down – with the reading head at the bottom. The long part of the scale was bolted to the T-slot table, using a couple of spacers to match the distance of the reading head from the lower part of the table.

While I was at it I also installed way covers, made out of the plastic concertina part of an expanding file. I also added a piece of thin aluminium angle to shroud the scale from the top.

I took the top two parts of the table off and laid them upside-down on a sheet of plate glass, and then aligned and punched holes in both parts of the table to mount the scales. Behind the reading head and also the long part of the scale are spacers which give the necessary offset to each part of the scale.

X-axis scales installed, and after a year or so of use. You can see the thin aluminium shroud at the top, and the spacers pulling the scale out from the T-slot table. The plastic way covers work remarkably well, although after extensive use they could probably do with replacement… You can also see the Y-axis scale below.

Y-axis scales

I installed the y_axis scales on the right side of the table, away from the gib and locking screws. I made up a two-part bracket: one L-shaped part screwed to the middle section of the table, the other L-shaped partscrewed to the reading head. This two-part design made it easy to align everything and mark out the screw holes.

As I installed the scale right-way-up (with the reading head at the top), I felt I needed more protection for the scales than the yellow plastic strip that opens and closes around the head as it travels up and down the scale. I ended up milling a slot into a piece of aluminium angle, and using furry draught excluding strips which fill the slot when it is not occupied by the bracket connected to the reading head.

This furry stuff is great – I can see lots of uses for it. I got mine from The Hairy Worm, a family business who manufacture the stuff.

Top view showing the two-part bracket, the aluminium top cover with its milled slot. The bits of fur poking through the slot are the draught excluder. The arrangement works very well – only a few bits of swarf have gotten through the fur and they were easily dealt with by the yellow plastic strips on the scales.

Bottom view showing bracket connection to the reading head. The fur came with a self-adhesive strip: I stuck one side to the aluminium cover (seen in previous pic), and the other to the adjustable stub of aluminium angle that you can see in the photo above.

The front way covers: apologies for the quality of the pic, however you should be able to see how it all holds together. I used aluminium strips screwed to the center section of the table (on the right in the pic), with the other side screwed to the top of the leadscrew mounting block. The dial is now difficult (but not impossible) to read, however I have not found this to be an issue, as I now have DROs!

DROs in use

I have used this set-up for a year and a half, including some very messy jobs… Apart from the problem with the Y-axis on the display packing up, the DROs have proved more useful and robust than I could ever have hoped. In fact, I was so pleased I went a little DRO-mad and also added them to my lathe.

KT 160×450 mill table rebuild

December 2014

My mill/lathe combo came with a ‘foot’ to attach it to the lathe, as well as a KT200 XY milling table. After struggling for a year trying to mill on the lathe bed, I finally gave up and made a workbench suitable for the mill head and the stand-alone KT 160×450 XY mill table.

However the KT mill table was in need of some TLC… it was covered in muck and sometime in the past someone had broken both of the handwheels (probably when trying to move it).

I had already disassembled the table during the lathe rebuild, for ease of storage and also to clean the worst of the muck off most of the bits.

Handwheels

The first job was to find replacements for the handwheels. This proved to be more difficult than I expected. The stock handwheels were 100mm diameter, had a 10mm bore with a 3mm keyway, and a 30mm diameter by 12mm deep boss. The dimensions of the boss appeared to be important, as the index ring ran on this boss – if it wasn’t the right dimensions then the index ring would be too tight or too loose.

Original handle

One of the original handwheels – twiddle me not. The boss part is broken off, visible at the top.

First I went to the usual suspects: ArcEuro Trade, Chronos and RDG Tools, but they didn’t have anything suitable. Next I trawled eBay, the best I could find were from this seller in China, and had a 10mm bore but a 4mm keyway. I ordered them and they arrived about a week later (dunno how they are managing this but delivery times from China are now one to two weeks, pretty impressive).

I chucked up the handwheel and set to work machining a new boss. The handwheels are made out of Bakelite, or something very similar. Top tips for machining Bakelite:

  1. use a vaccuum, the dust from Bakelite is carcinogenic
  2. don’t use your best cobalt cutter (ask me how I know) – use an unfavourite HSS tool, a sharp/pointy tip and zero or negative rake, expect to sharpen it many, many times… and then sharpen it some more…
  3. use a vaccuum, the dust from Bakelite is carcinogenic

Machining Bakelite is a bastard. Makes a hell of a mess, and blunts tools on sight. Light cuts just cause the Bakelite to melt and harden, and blunt the tool even faster. Heavy cuts get under this layer and remove a lot of material. I would get one good pass with a heavy cut, then remove the tool for sharpening…

 

turned replacement handles

After an hour of machining, and many long hours regrinding tools… The Boss arrived. Before and after pics, the second handwheel is ready to be chucked up and frustrate me.

Handwheel installedHandwheel installed, showing the index ring.

Cleaning and mending

Next I cleaned up all the bits with petrol and a green scourer (for non-way surfaces), cleaned the holes with a pipe cleaner and blew them out with compressed air. It was all going so well until I turned over the t-slot table and found surface rust underneath.

I scraped as much off as I could, very carefully and gently, with a blade. After some inspection and head scratching I realised that the surface rust was not on the ways, but instead on the other surface (the not-way). After scraping the surface felt very smooth, no pitting at all and the machining marks were still clearly visible. In the end I rubbed it down gently with some oil and fine emery paper, and left it at that.

While not ideal, I think that even if this rust had been on the ways it would not have caused too many problems. I am not expecting supreme accuracy from a mini-mill.

rust before scraping

Before (above) and after (below) pics. Even in these photos you can still see the machining marks.

rust after scraping

During the rust removal I noticed a couple of small dings/dents on the pointy part of the dovetails on the t-slot table. They were both at left end of the table (furthest from the handwheel), so I guess they got damaged because they were exposed, hanging out over the edge of the base. This damage may have happened at the same time the handwheels were broken.

I got out my blade and emery paper again, and gently sanded away the raised parts. I tested that it was flat by running the blade over the dent – when the blade passed over without catching anything then I stopped sanding.

Sanding ding

Sanding the dent: there is a knife blade wrapped inside the emery paper to keep it flat. Ground stock would be better if you have some. The dent is visible just above the emery paper.

Assembly

The rest of the build went smoothly, there are not many parts and even without a diagram it is easy to work out where everything goes. I lathered the ways with way oil, then cleaned up the mess I had made… the leadscrews I lubricated with the same way oil.

The only thing that still stumps me is the length of the gib screws: they stick out about 20mm. Also it would make more sense to have slotted or square ends rather than a hex bolt head, as it is difficult to get a spanner over the gib screws on the lower plate.

Before and after:

Table - beforeTable - after

And again:

X-axis - beforeX-axis - after

Mill head inserted and ready to make some chips:

Finished