Groovy Grief

A

Allan

Active User
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Hi.
I've been facing a block of hot rolled (A36?) in my 4 jaw to make a square block. It has turned out amazingly square so far. The ongoing problem that I can't seem to beat is that instead of getting a reasonably consistent finish, I get "grooves" for lack of a better term. THey tend to be ib the inner inch or so. Once I move out toward the outside things get much smoother. I have tried adjusting the cross slide gibs which yielded some inprovement but still not what I'd like to see. Also the cross slide gets hard to move. Methinks that can't be good. Any ideas? Thanks in advance.

Al
 
Some thoughts:

Are you using any lube like WD-40 or cutting oil? Is swarf getting caught up on the bit? Also, how big is the piece? As you get toward the center, the SFM naturally decreases so, start out at a higher RPM and decrease feed as you get toward the center. Are you starting from the center and working outward or opposite that? Is your compound backing out? Keep an eye on the dial to see if it's spinning. Are the rings/grooves happening at the same radius as the intersection from where the cut goes from continuous to interrupted?

BTW: What's the material, type of bit and other parameters?

Ray


Allan said:
Hi.
I've been facing a block of hot rolled (A36?) in my 4 jaw to make a square block. It has turned out amazingly square so far. The ongoing problem that I can't seem to beat is that instead of getting a reasonably consistent finish, I get "grooves" for lack of a better term. THey tend to be ib the inner inch or so. Once I move out toward the outside things get much smoother. I have tried adjusting the cross slide gibs which yielded some inprovement but still not what I'd like to see. Also the cross slide gets hard to move. Methinks that can't be good. Any ideas? Thanks in advance.

Al
Click to expand...
 
A couple quick thoughts about interrupted cutting:

1) Warning! If you have a spin-on chuck, every impact is tightening the chuck a little and you may struggle dearly next time you try to remove the chuck. Take light cuts to save both the bit and yourself from a great ordeal. If you have a lot of it to do, loosen the chuck after every piece to make sure it's not getting hoplessly screwed tight. (ask me how I know).

2) Sometimes it's hard to make a cut of proper depth with interrupted cuts (such as with a square/rectangle shape) because it's hard on the bits. The solution: Make a light pass of just the interrupted section then, crank the x-feed back, dial in a little more depth then make a full pass. This way, at least the center portion gets the benefit of a decent cut with a good engagement.

3) You're almost always going to see some rings where the cut goes from interrupted to continuous because the bit needs to re-establish it's position once the interrupted part is over. This is true of lighter duty lathes and especially true with carbide. EDIT: If the piece has a hole in the center, there's nothing wrong with working from inside to outside and this will get rid of the little ridge that happens when you go the other way. Just don't cut too deep at the interrupted part because it eats bits. If you have carbide, use C2 (more flexible and not as hard).

4) With interrupted cuts on a block (which is really just a face cut) lock the carriage and adjust depth with the compound.


5) LOL: Use a mill if possible.

Ray
 
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