5c Indexing Collet Fixture trouble

[SmokeWalker]

Hey everyone,

I've got one of these:

http://www.shars.com/horizontal-and-vertical-precision-5c-collet-index-fixture

And I'm using it to make circumferential slots in a part with an end mill; plunge milling to start the slot, and then slowly indexing it to form a few circumferential slots.

When you've completed the entire circle, the spot at the beginning of each slot where the plunge was initiated is ever-so-slightly to one side compared with the rest of the slot; as though somehow the part is pulling forward for the moment of the plunge, and then once the (side) milling commences, the part is pulled backward, making a slopply slot.

Any ideas what I should/could do to fix this?

SW.

 

[Ulma Doctor]

Hi SmokeWalker,
you may be able to use a smaller endmill to initiate the annulus, then use the finishing size to complete the operation.

 

[Asm109]

Use a reground endmill and step it over to make a 2 and 3rd pass to bring it to size.

 

[Bob Korves]

Both of the responses above are on the right track. Plunging an end mill often leaves a hole larger than the end mill diameter.

 

[SmokeWalker]

Hi SmokeWalker,
you may be able to use a smaller endmill to initiate the annulus, then use the finishing size to complete the operation.

Use a reground endmill and step it over to make a 2 and 3rd pass to bring it to size.

I understand what you're saying, but the issue isn't with the mill. The indexing fixture is pulling itself back at the beginning of each cut, leaving an L shaped slot instead of an I shaped one. Removing and remounting the end mill, or reshaping it won't change what is happening.

Has anyone tried to do this with an indexer before?

 

[Ulma Doctor]

i have not seen that before.
can you take video?

 

[JimDawson]

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.

 

[rzbill]

Removing and remounting the end mill, or reshaping it won't change what is happening.

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.

 

[Billh50]

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?

 

[Larry Hoy]

I have been cutting a bunch of slots the last few days and have found that if I slowly advance the plunge cut it helps.