Ridges on milled surface

[skippyelwell]

I'm removing a lot of metal a little bit at a time on the mill using a 5/8" roughing end mill with rpms at about 700
On the X axis the surface is smooth and can feel no difference between passes, on the Y axis there are ridges between passes
almost like the cutter is digging in on the left hand side.
Each pass is cut in the opposite direction as the one next to it, I made sure the cutting bit is 90* perpendicular to the table.
Could this pattern indicate slop in the gibs of the Y or Z axis?
I adjusted all 3 gibs as best as I could, if anything they may be dragging a bit too much.
The drawing is an exaggerated depiction of the surface in the Y plane.
Thanks

 

[Martin w]

Looks like your mill head or knee is nodding forward. Do you have the knee clamped when you are milling?
Martin

 

[skippyelwell]

Looks like your mill head or knee is nodding forward. Do you have the knee clamped when you are milling?
Martin

You know, I might not have. But if the knee was tipping forward why would the slope of the cut be towards the left in the X plane?

 

[Susquatch]

I think your tram is off too. But it could also be an artifact if using a roughing mill. Sometimes they don't cut the same way climbing vs conventional. So I'd also recommend trying to go the same way on each pass and see what happens. In other words, make a pass, crank off the work, go around, and then take another pass the same direction as the first.

One of the issues I faced tramming my Bridgeport Clone was getting enough distance to accurately set a good tram. Particularly for nod which has to use the narrow part of the table. That's one of the reasons I decided to make myself a good 3-way tram fixture.

Also check your vise. Is it really square and level? And does it pull the work down square and level?

 

[trevj]

Try a 2 flute mill.

Think of it this way, as the cutting flute sweeps across the work, the flex in the milling cutter itself, as well as any play in the head and bearings, causes the one side to dig in, making a sawtooth profile on the surface. Pretty much the reason you use a two flute mill when you want the slot size to match the end mill size, instead of being mildly to wildly, bigger.

I taught the folks I taught, to learn to recognize which direction and rates that gave a better finish, and to use it to advantage as best they could.

For what It's worth, I always found that a mill that was just a 'tiny' bit out of tram, could be relied upon to make a pretty decent finish pass, as the deeper trailing cutting flute, left a series of smooth scallops on the profile, rather than the ragged sawtooth.

Edit to add: Oh yeah. Workholding. Cut or make some shorter studs, and try to keep your hold downs below the finished surface plane, and you can then do all the finish passes in the same direction, whichever that is that works to give you a nice finish. Keeping the conditions the same, is a large step towards keeping the finish level the same over the work.

 

[skippyelwell]

I think your tram is off too. But it could also be an artifact if using a roughing mill. Sometimes they don't cut the same way climbing vs conventional. So I'd also recommend trying to go the same way on each pass and see what happens. In other words, make a pass, crank off the work, go around, and then take another pass the same direction as the first.

Will do.

One of the issues I faced tramming my Bridgeport Clone was getting enough distance to accurately set a good tram. Particularly for nod which has to use the narrow part of the table. That's one of the reasons I decided to make myself a good 3-way tram fixture.

I didn't use my dial indicator to test, just set it using a square. I'll do it properly and report back.

Also check your vise. Is it really square and level? And does it pull the work down square and level?

Not using the vice, work piece is fastened to the table itself.

 

[Proxule]

 

[Susquatch]

You know, I might not have. But if the knee was tipping forward why would the slope of the cut be towards the left in the X plane?

I think the cutter tells you what is what. So reading what you are saying, if the slope is high toward the left, then the head is rotated clockwise.

But again, sometimes roughing cutters do weird things. Try a regular endmill before you adjust anything.

 

[skippyelwell]

So I tried a 2 flute end mill first to see if it was an artifact of the roughing bit, nope, still tilting to the left.
I cut a section cam rocker rod I had left over from a BMW engine rebuild and mounted it in the spindle.
Pulled out my new toy from the auction a few weeks back, a cylindrical square and yes, the head was out of alignment.
Tapped it back into place and milled a few lines, smooth as can be.
Thank you gentlemen, much appreciated.

I only have to remove 1 more mm to bring it down to the right height but I'll wait and do that with the fly cutter I ordered today.

 

[Jswain]

Looks awesome!!