ML7 restoration

[Joachim BakkeParticipant @joachimbakke98156]

I have finally put my ML7 on the table. It is not in good condition

[Joachim BakkeParticipant @joachimbakke98156]

Hi all,

I have bought an ML7 many years ago, and it had been used in a student workshop. After a few moves, I have it back here with me and I'm starting to think it is more than cleaning and oiling required.

The chuck is stuck. I just broke two boa grips trying to loosen it from the spindle.

Worse, the spindle bearings are gone. There is not much wiggle when the motor is disengaged, but when I engage the motor lever, I get 0.5mm (sorry metric) lift. I assume that is more than removing a few shims can alleviate?

I have nor removed the bearing housing, since my metric allen wrenches do not fit.

[HopperParticipant @hopper]

Be careful removing that chuck. It is easy to break a tooth off the back gear if you use that to lock the spindle while yanking on the chuck.

One way of removing a stuck chuck is to cut a piece of hardwood to fit on the bed and stick up enough to catch one of the chuck jaws as it is rotated in the reverse direction. Then open the belt guard, put the belt in the low speed direction and by yanking on the belt rotate the spindle in the reverse direction, rotate teh chuck briskly until the jaw hits the hardwood and jars the chuck loose. It's best to do this with the power unplugged while handling the belts of course. If you have a reversing switch, and get desperate, you could even set the jaw away from the wood block and start the motor up briefly to rotate the chuck under power until the jaw hits the wooden block. Again, be wary of doing this in backgear as the teeth are prone to flying off under abuse.

With .5mm (20 thou) movement in the spindle, you might, maybe, be able to eliminate it by removing shims. Mine had a bout 15 thou of shims in there when I got it. Some scraping of the bearing to fit the spindle may be required, using bearing blue and a curved half-round scraper. If you are lucky most of the wear will be in the top half of the bearing, due to belt tension direction and cutting force direction. It might be necessary to file or machine down the mating faces of the bearing cap and lower half if there are not enough shims to remove. You can't buy new bearings. Only the full hardened spindle and bronze bearings as a kit, and quite expensive. Or used spindle and bearings from eBay. (Possibly someone else's worn out junk!)

If you have access to a milling machine you could machine out the bearing housings and install tapered roller bearings. I think Alan Hearsum published an article in Model Engineer about this conversion some years back,

Edited By Hopper on 03/02/2017 23:13:49

[roy entwistleParticipant @royentwistle24699]

Joachim You will find that nearly all the nuts and bolts will be imperial ( BSF, AF, Whit etc )

Edited By roy entwistle on 04/02/2017 10:41:01

[Joachim BakkeParticipant @joachimbakke98156]

Thank you both.

Roy, I am ok with imperial. Managed to get some imperial allen keys.

Leaving the chuck for now, I decided to have a look at the bearings. When I loosened the bolts holding the bearing housings down, I noticed they were quite slack to begin with. Bearings looked quite ok, still some white metal left. I then bolted down tight to see, and the play was now reduced to less than 0.01mm when I engaged the motor pulley. I have some stuarts blue in order, so I'll wait with any further action until I can look at the fit.

How can this have happened? I'm thinking someone opened the bearings and removed too maúch of the shimming, and then left the bolts with some slack that may have developed over the years?

I should probably have some shims ready as well, in case I have to lift a bit more?

Where can I find a proper guide to fitting and aligning the bearings?

[Joachim BakkeParticipant @joachimbakke98156]

Hopper, the method I used was to sneak a boa grip under the first gear just aft of the chuck, and try to turn the chuck with a spanner. But the reinforced rubber band of the boa grip tore off. Twice.

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