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

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