A scraping project

[J Tiers]

I deided to just make a thread of this instead of disjointed posts in "what did you do today".

I started re-scraping a portable slideway I have, so it can actually be used. Fits were crummy, it blued like a piece of the Ozarks, and it clearly had worn at one point to where the slide was riding on a surface not intended to ride on. That had been repaired partly by planing down the dovetail on the base that it was riding on. Apparently the other way surfaces were either ignored or just milled and called good.

Toolholder t-slot surface (on crosslide), after some scraping... it blued in two corners originally. Gonna take some more work.





Cross-slide surface of the "carriage". Early, about one scraping pass. Nice visible "as-milled" surface for the slide to move on.....





The shiny spots it was, but is not supposed to be, riding on. The flats to the side are where it should ride.





Decoration apparently applied as compensation for the crummy slideways... ?????

It was on the top of the crosslide also, and pretty deep.

[J Tiers]

More pics and stuff

The slideway base, about 18 inches or so long. Leadscrew for it is in the background. Big 'ol lantern toolpost from it in the yellow box.




The planer marks, which might actually be from a roughing cutter, now that I look closer.




The underside, has a pattern of holes on it for fastening down. A leadscrew and nut moves the "carriage" and crosslide along.

[J Tiers]

After working on the second surface for a bit, I decided that it was just not going to "come in", because there was a good sized dip in it, and it was not, as I had thought, going to be washed out when the surfaces on top and bottom were aligned.

So I decided to mill off some of the surface.

Here is the first pass of a couple thou. You can see the edge was way lower than is practical to fix by scraping. Scraping, even working hard and making the dust fly, takes off only a couple tenths at most. To get the surface to "come in" by "scraping straight down" (evenly over the surface) would take a long time.




First and second side done. I used a long ball-nose end mill, because I needed it to do the whole surface in one pass. Making multiple passes would complicate things in ways I just did not want to deal with, and I was too lazy to put on the vertical head and use a different tool.



After working on it for a while, I got to this point, which I decided to call good for the moment. It is getting 10 to 15 points, which is reasonable for a surface which is actually not an active sliding surface. This is the crosslide, which is moved only to change the cut depth, moves under an inch total, and is static most of the time. I can always come back to it if I so choose.




So, on to the next surfaces.

[JoeLee]

Don't you get a lot of tool deflection side milling with that long end mill??
It also looks like there are some coolant stains on the one piece in your second picture. That alone shows that there is a gap between the two surfaces.

I'm also wondering .... why did you choose to mill it that way?? finish?

I'm going to have to go back and read your post from the beginning.

I have an older Craftsman X Y table that someday I would like to go through. This is a good lesson.

JL.............

[reggie_obe]

If available, wouldn't a face mill cutter be a better choice?

[JoeLee]

My thought is side milling with an end mill creates a nice even wave type finish with high and low spots with good consistency.

JT's second and third picture show that quite well.

JL...............

[J Tiers]

Those stains I am not sure about. But those were not the areas that were low. The problem area was actually at the righthand end of the milled surface in the first pic of post 3.

There is little deflection. The end mill is cutting pretty close to the base of the flutes, and since it is going to be scraped anyway, a small deflection is no issue. The point of it is to eliminate the big variations. It cleaned up across the surfaces in a couple of scraping passes, even though it did blue ip in a line down the inner.edge of each surface. The end mill is way longer than it needs to be, but is not being used near the end. It was the one I had handy that was long enough to cut the full surface, and fit without changing the holder that was already in the mill.

Yes, a slow feed gives a gently wavy surface that is good for scraping. You can see in the pics that the waviness is considerably less than the original surface had, and it was easy to get through it. Using a face mill would also involve standing the work up, with much adjustment to ensure getting a consistent thickness. Laying it down on the table tends to keep that inherently under control, and is dead easy to do.

I am going to have to mill down the surface of the male dovetail on the crosslide, as it will now rub, due to wear in use added to the reduction in height of the female dovetail from scraping and milling down to a flat surface. Same reason the long part has the dovetail milled down. There may be other areas that need relief as well, we'll see.

Normally, one would do some sort of survey of issues, to develop a "strategy" of scraping, but this piece is so simple, that I determined to essentially just "have at it". It was also fairly dirty, and would have required to be disassembled anyway for cleaning. With luck, the crosslide screw will be OK as to location, I really do not want to have to move it a few thou, unless that can be accomplished hy adjusting the position of the mounting bracket. It threads directly into the body of the crosslide, there is no separate nut for it. A separate nut could be shimmed, or cut down as needed to adjust position.

[Peter.]

If you stood the part on it's edge and milled it with the end of the end mill, you could have used a shorter, larger diameter cutter and the result would not be affected by any possible table droop.

[J Tiers]

If you stood the part on it's edge and milled it with the end of the end mill, you could have used a shorter, larger diameter cutter and the result would not be affected by any possible table droop.

Actually it could make the droop problem worse......

The upper surface could be milled to a different thickness due to any lean away from the cutter. There might be an added issue if the surface of the part that touches the table is not perpendicular to the existing scraped surface, which would put the surfaces out of parallel. Part of the goodness of the method is that it avoids that issue, and makes both portions the same. and, it does not depend on any un-machined surface that may not be flat or perpendicular. If there is a slight tilt, it is the same on both portions, and will be removed in the scraping process. The part will more likely end up with the top and bottom surfaces close to parallel.

[reggie_obe]

If you stood the part on it's edge and milled it with the end of the end mill, you could have used a shorter, larger diameter cutter and the result would not be affected by any possible table droop.

You have a horizontal mill, why not a slab mill?

[J Tiers]

So, doing the bottom of the "saddle" part, I found the same issue of a big wear area at one side, possibly because the saddle piece does not have any wipers. So same routine of the mill. this time I took off a total of 6 thou, You can see in the first pic the rolled-off end that the arrow points at. As per the note, this was after taking off two thou from the worst side.

The table has some slop on the feedscrew, but I was able to climb mill by pulling the table into contact with the feed screw while cutting, so that the screw was basically regulating how much the table moved, not moving it. Made me think that I might get away with climb cutting if I hung a weight to keep the table in contact with the screw, so that it never would have room to move from the cutter forces.



After that side was done



Both sides



Part of the pile of swarf from the 6 thou off. Just the part that stayed on the table.

You have a horizontal mill, why not a slab mill?

I would have used that, but it was easier not to chage it around that far..... the slab mills are overkill for this small job.

[Peter.]

You have a horizontal mill, why not a slab mill?

Because table droop is going to affect the part no matter what you do.

Bending away from the cutter is a setup issue, not a problem inherent to the methodology. If you block it stiff enough and square it to the cutter then face milling it on the horizontal should give you pretty good geometry for scraping to finish.

[J Tiers]

Depending on what you mean by table droop, the slab mill is probably the best plan. It is actually knee droop that will cause issues.

The problem with setting up to face mill with a horizontal mill is that the "reference surface" that you will have contacting the table has NO necessary relation to the surface you are machining. It is just the side of the part, probably generally perpendicular, but not necessarily so accurate. Why spend a lot of time making it square the hard way, when the machining is essentially a "roughing pass" which will be finish machined by the scraping?

Potting one way surface in contact with the table, the topside can be machined parallel with it to a decent accuracy, better than relying on an unknown surface. Using an end mill is essentially the same thing as the slab mill, even to the cutting geometry, it is simply a smaller diameter, and not as well supported. A second pass, climb milled, acts as a spring pass and reduces the effect of deflection, which is already relatively small for a shallow cut of a couple thou.

But it makes little difference, the errors of alignment are such that they are easily corrected by the scraping.

[strokersix]

Can you use a center in the end of your long endmill for support? Can't tell if it has a center from the photo.

[Peter.]

Depending on what you mean by table droop, the slab mill is probably the best plan. It is actually knee droop that will cause issues.

Tables tend to droop at the ends especially on older or more limber machines. If you put a part on the table and traverse the table the motion will describe a shallow arc rather than travel straight. One of the things we learned in the scraping class was if you want to machine a camelback casting on a knee mill prior to scraping, don't mount it on the table standing up, but block it up on it's side with the face you want to machine towards the column. Then, so long as the ways are good, you will mill it straight rather than bowed as would happen if the table suffered any droop at all.