Its not clear to me that you do understand what the folks are trying to say.
Changing to a multipass operation with a smaller set of cutters. First a roughing then finishing cutter WILL change what is happening. The rough pass may exhibit the J but the finish pass should not.
That's not a bad suggestion, but even if the end mill were the problem, switching back and forth between end mills is a lot of hassle for this.
i have not seen that before.
can you take video?
Are you using a 2 or 4 flute end mill? A 4 flute will walk sideways when cutting a full width slot giving a pretty pronounced ''L'' at the end of the cut.. A 2 flute is somewhat less prone to doing this, depending on the feed, speed, and DOC
If you can't feel any axial play in the indexing fixture, I would be surprised if that were the problem. Put an indicator on it while cutting and see if it's moving.
I have used these hundreds of times through the years. Some of then many years old and have never seen this happen. What I have seen are 2 things. Table movement and endmill or spindle flex. By roughing and finishing this usually fixes the problem.
You keep saying it is the indexer moving. Have you put an indicator on the face to prove this? Or how are you seeing this?
If nothing moves and nothing flexes, you would not have a problem, correct? So it’s moving and or flexing, probably? You need to find it. And sorry, not enough info. What kind of milling machine? What size cutter? What’s the material? To name a few. Sorry again, all you will get is random guessing without more info. And it’s very hard to resolve this kind of problem without seeing it happen in person…Dave.
That type of indexer just has a solid cone bearing/bushing. It needs clearance or it will not turn. It’s not like a ball bearing set-up with preload so there is no end shake. It needs clearance to turn! So you will have some end shake. But if properly adjusted, I don’t think that is the problem. I can your process working, but feed control with your hand can be hard on the end mill and hard controlling finish. I would use a rotary head with crank.
HF Mini Mill, 3/32" 5º tapered WC end mill, in acetal at 3,000 RPM thereabouts.
Thank you for all the suggestions, ladies/gentlemen. Some very methodical thinkers visit this forum. It's a great place to be.
After a bad night's sleep, I woke up at about 4am and thought that I should put a DTI on this to see exactly when/where it's moving. I'd take a video of this, but I don't have a good way to hold my phone steadily enough while doing this, and I have a feeling that in the video, you'd never be able to see what's happening between my hand shaking or the lack of a macro lens.
Last night I measured the slots on the test part and could tell it was moving about .006; when I tried indexing the gadget with no part in it,
I could visibly see the spindle sliding outward when I press the lever into the "pin" that begins the indexing process; .006 is painfully visible, but might not lend itself well to being captured in motion picture.
When I looked at my DTI on the machine this morning, here's what I could determine happens.
- You press the lever, engaging the pin and depressing it.
- The indexing head immediately slides outward (away from the direction of the pin depression) about .006.
- You slowly begin pulling the lever around the fixed portion of the circle of which the slot is cut (in my case about 4/24 of a circle)
- About 2/3 of the way from the detent on which you began to the next detent, the spindle abruptly slides BACKWARD to it's initial position. (There's a big silver hub right behind the main casting with 24 evenly spaced notches that tell you which detent you're on.)
- As you proceed with the cut, the spindle of the fixture stays steady and allows you to cut a straight slot–not an "L"-shaped one.
- This happens essentially at every instance where the lever is engaged.
So, using my DTI to tell me when exactly the
pop out and the
pop back occur, I marked on that silver hub exactly the moment when (where I want to make my cuts) the spindle pops back to it's original position, for each of my slots, and tried making the plunge cut ONLY after the spindle has returned to its resting (pop back) location. Smooth sailing, no L shaped cut.
I think Chips&More's comment with the cone "bearing" is the explanation.
The rotary table is a good idea, but not nearly as convenient because I can program this thing to cut up a circle any way I want in sections of 1/24, but a rotary table can only handle one division at a time.
I suppose now to get the sort of slots I want, I just need to dial in exactly the right depth of cut, and the right stops in the fixture.
Any thoughts?
