Scraping a-way (on my micro mill)

[Iain DownsParticipant @iaindowns78295]

So. For a variety of reasons I'm trying to get my little CMD10 tuned up.

The problems I've identified so far are that

The Y movement is sticky, either due to a bent gib or a dodgy way. I'm measuring a 0.01mm blip on one of the ways in about the right place so maybe that's it.

The front of the table is 0.1mm lower than the back which appears to be due to there been more metal between the way and the table at the back.

The mill needs tramming, but when I do so and get some accuracy it doesn't seem to keep it.

I decided to have a go at some scraping and picked the top way of the Y slide. Mainly because it's the only one which is on top that I can easily get to. I thought that scraping into the dovetail was not the best place to learn..

So I set to. I've spent about 8 hours now on two bits of iron which are about 15 square cm each and I'm not entirely sure I'm making any progress.

Having re-read some MEW forum posts and re-watched some you tube I changed things around this afternoon. The first thing I did was to switch to putting the blue on the table and not on the way. I liked this because it seems to give a more 3D effect which makes it easier to spot higher spots.

I also ground the scraper into a mild arc and put a 80 slope on the end. The scraper arrived flat and square and I suspect that I've been scoring things badly with the edges and not taking off the right bits.

Here are two 'time-lapsed' pictures of where i've got to today. i'd appreciate any helpful comments. The gap in the image is where I changed my approach.

Non-Gib way

Gib Way

I *think* that I'm finally showing some progress. The last set of (8) images took about 45 mins to scrape and it's the first time I thought I might be making progress.

Some of the ways on this little think quite clearly show milling marks, so it's not been made to the highest standard of precision and I do wonder if I'm wasting time on this…

Iain

[Iain DownsParticipant @iaindowns78295]

[HopperParticipant @hopper]

Oh boy, can o' worms ahoy!

You probably should sit down and read the book "Machine Tool Reconditioning" by Connelly. It is basically the scraper's Bible.

There is more to it than mere contact area. You need to be sure that everything is staying flat and square as well. Usually one would start by knocking the burrs and high spots off everything with a dead smooth file and see if that helps.

Then as far as scraping goes, one would most often start by scraping the fixed bed ways flat against a known flat surface plate, a small one that can be lifted on to the job. At the same time you have to make sure the ways you are scraping are aslo dead square to the vertical ways (z axis). Depending on the shape/set up of your mill, this might require a scraped square or at home you might use a good quality try square clamped to the way and run a dial indicator up and down it attached to the quill (which must be of course free of excess play).

Then once you have the flat surfaces of the fixed ways flat and square in two directions, you might use a scraped prism to scrape the dovetails flat, and using a pair of rollers and a micrometer, parallel.

Once you have that all sorted, then you are ready to blue up the fixed ways and scrape the moving ways on the table to match.

It is a lot of work and as you are beginning to realize, of questionable worth on a cheap machine.

You say you have the front of the table .1mm lower than the back, due to more metal at the back of the table. The cure for this might be to take a cut with a flycutter over the top surface of the table, after you have first made sure the fixed ways on the bed of the machine are not the cause of the problem. Proceed with caution, and measure everything several times before taking drastic action such as this.

The lack of ability to hold true after tramming indicates something is loose somewhere. Maybe the column is not secure, or is too flimsy and is bending? Is the head the type that can be angled? If so, it may need pinning in the true position as they can tend to move under load. You cant really proceed with scraping until you have the z axis set right, as all ways need to match it.

Edited By Hopper on 27/06/2016 05:52:10

[Ian S CParticipant @iansc]

On another forum, one bloke sorted his vertical mill, first he trammed the head, then he fitted a cup wheel(grinding)in the spindle, and used this set up to grind the surface of the table, took a long time, fractions of a thou each pass. Ian S C

[MWParticipant @mw27036]

Have you checked out the feed nut and lead screw? sometimes you might have a hefty chunk of debris stuck on there. It does go through alot of grease.

The scraping looks good though, keep up the good work, practice is the best remedy for hand skills.

Also like you said, check the gib itself because this would have a major effect on it's movement. The tightness of the grub scews can make a big difference.

Michael W

[Iain DownsParticipant @iaindowns78295]

Thanks all for comments.

My main objective was to see if the scraping was actually working. I couldn't help but feel that I was more moving the peaks around than actually reducing them. Michael – thanks for the encouragement. another 30 minutes today seems to be moving (VERY SLOWLY) towards smaller islands. Mainly.

Hopper – my mill has a bolt on vertical it will be a lot easier to scrape the ways for the table square and tram the head with shims. Which seems to kind of work. It I was going to start at the bottom I would remove the base and put that on my surface table – the base is a lot lighter than my surface table (which isn't that big!).

I'm not persuaded that I actually want do do all of this (particulary on my little thing), but I surprised myself by actually enjoying the scraping. I want to get this surface to a decent point so I can re-assemble and check gibs and things. I may end up just scraping any obvious high spots.

To give you some idea of the ways, here is a photo of the lowest set of ways. To be clear. The way is NOT the smooth surface on top but the rather badly machined surface lower down in the dovetail.

The way on the table is worse.

Ian I like the idea of a grinder, it may work better for me than trying to fly cut the table as Neil has suggested.

Micheal, the lead screws and nuts are fine – the binding happens with the lead screw out completely.

Iain

[MWParticipant @mw27036]

I know this may be way off into the future but you could consider fitting rubber bedway wipers onto the mill after you're done, should help with the movement by preventing the ingress of swarf.

Michael

[JonParticipant @jon]

Think should be treated scraping as some sort of oil retention rather than accuracy.

The only decent quality stuff is precision ground some with scraping some not.

Reason chasing the high spots around is because taking too much off. Seen this rooks of times and wish had a tenner for each that said only took 4 thou off. Its too easy to take 10 thou chunks time and time again that could take 80 thou off to put right, as Hopper says tip of the iceberg one flat surface still could be way out but flat!

[Iain DownsParticipant @iaindowns78295]

HI, Jon.

How do I take less off?

I'm scraping the surface and I would have said I was taking fractions of a thou each time. I'm putting little pressure into it and trying my best to follow guidance from web and you tube.

But clearly I'm not at all sure I'm doing this right, so any pointers would be most gratefully received!

Iain

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