[dalianharley]

Hi all,

I was countersinking 8 existing 12mm holes to 17mm top diameter on a 3mm thick cold finished steel plate, first with a 3 flute 90degree HSS countersink bit, then a 6 FL 82 degree HSS countersink. Only half of the holes came out to be alright, the other 4 all had some chatter and the holes are rough. My feedrate was 2.9, i tried both 500 RPM and 1000 RPM at the rate, all came out to be the same. what's funny is, all the holes that were finished smooth stayed smooth at different settings, those chattered always chattered. Could it be my holding is weak? the plate is located with roller pins then a small toggle. I was thinking adding another toggle.

Suggestions?

thanks

Daz

[johnedward]

use as low rpm as you can with good support under each hole, a piece of wood underneath will work.

[TurboStep]

Like I tried to explain in your earlier thread;
http://www.cnczone.com/forums/tormac...ml#post1495892
use a chamfer drill mill and run a 2D contour to chamfer the edges. I NEVER "countersink" on my mill by simply ramping down.
Here's an example of an M8 countersink from an old prototype made using a chamfer drill mill:

Attachment 240602

And with the screw:

Attachment 240604

Edit: I think this was made with a 1/2" drill mill.
Step

[Hirudin]

I always do a circular path to countersink as well.
That said, it looks like a few of the holes worked just fine. As johnedward pointed out: the less well-supported holes seem to be much worse. Perhaps rotating your fixture (and code) 90º would fix that issue.

[tmarks11]

It is hard to tell without a side-on view of how you are supporting your work piece, but I believe that it doesn't have enough support and is flexing. Clamp it down to a nice piece of (sacrificial) aluminum stock (or even just MDF) to protect your table, and try again. Holding a thin piece up above the table like that is asking for problems.

[dalianharley]

step now your previous post made more sense to me - I didn't know enough to appreciate the contents.

is the reason you use chamfer instead of countersink due to the limited HP on tormach? Or it's a general practice on all CNC's.

to the supporting part - I do have a alum plate with roller pins and pre-drilled holes to give room for the countersink bit. I'm clamping the plate on my vise and I'll try to move it to my table instead. i think using the vise to hold it is part of the chatter problem.

[RussMachine]

Hey guys, did the Forum get hacked?
All of the threads are now closed. And there's a strange "PAID SPONSER" thread at the top of the TORMACH Forum.
What's going on ????

[SCzEngrgGroup]

Hey guys, did the Forum get hacked?
All of the threads are now closed. And there's a strange "PAID SPONSER" thread at the top of the TORMACH Forum.
What's going on ????

The entire 'Zone has been massively screwed for several days now. Logins don't work reliably, threads get closed for no reason, threads show unread posts, but when you try to read them, they don;'t show up unless you open the thread, then do a refresh. Paul (admin) has been working on if for days, but so far it has only gotten worse, especially over the last 36 hours. I believe this makes about 4 days it's been screwed up.

Regards,
Ray L.

[victorofga]

and it still not ended..

hope they can fix it.. this place put many beginner on cnc path.. thinking on the difficulties I had around 95-97 without internet, and no one around to asking, this forum is a blessing..
I thinking on to start to sponsor the forum..
I can give little, but if many gives little, then on the end might paul can be more selectable where he accept support from..

================================================== =================

in the shop I worked before 93
we made countersinks on the radialpress..
that had very low rpm's

some toolmaker put a piece of sanding clot under drillbit and it worked..

but the low rpm always.. 60-80 rpm..

of course with cnc it don't need anymore.. I like that solution with spotdrill..

[mountaindew]

step now your previous post made more sense to me - I didn't know enough to appreciate the contents.

is the reason you use chamfer instead of countersink due to the limited HP on tormach? Or it's a general practice on all CNC's.

to the supporting part - I do have a alum plate with roller pins and pre-drilled holes to give room for the countersink bit. I'm clamping the plate on my vise and I'll try to move it to my table instead. i think using the vise to hold it is part of the chatter problem.

IMHO drilling is the most violent of mill operations I have experienced. Also by far the most used cnc operation I program
My opinion is why ram a counter sink bit or any cutter into parts or material with a cnc machine.
I try to use the tool and its technology to complete operations reducing stress on part, cutter and mill and still get the job done with precision.
Again imho ramming speed is for old school equipment like manual mills that you crank wheels on not program with precision paths!

My experience, If there is vibration of the material "felt by touch" then its not clamped or supported well or correctly and precision and finish will suffer and or be dangerous.
md

[MFchief]

Although I agree with Turbostep concerning the best way to do countersinks on the Tormach, I have alway had better luck countersinking using the single flute style in the photo. Even when drilling by hand on the drill press this style seems to have less chatter. The one in the photo is well used and about ready for replacement, or grinding.

BTW, I also have been having a weird issue with the forum the last few days, couldn't see any post newer than 17 june, but Paul at admin solved it for me. Clearing my browser cache fixed it.

Terry

[TurboStep]

...is the reason you use chamfer instead of countersink due to the limited HP on tormach? Or it's a general practice on all CNC's...

General practice? No idea. I was never really a fan of countersinks, probably due to using them incorrectly in the past. If guess if you use the right bit for the job, the machine (and workholding) is rigid enough to avoid the characteristic chatter, the chipload is kept high enough and the chips can be evacuated effectively then they should work fine. The larger the countersink, the more difficult this is going to be (and you're using quite a large countersink).
Chamfering simplifies the whole thing significantly and enables the outside diameter (the small counterbore on my first image) to defined freely. I prefer to use the capabilities that CNC offers me in order to overcome, or avoid such issues.
The single flute countersink posted by Terry looks like a very interesting alternative to help eliminate chatter.
Step

I've nothing against countersinks, i just hate 'em

[tmarks11]

I also have been having a weird issue with the forum the last few days, couldn't see any post newer than 17 june, but Paul at admin solved it for me. Clearing my browser cache fixed it

Safari and IE don't let me log-in to the forum, even after clearing my cache.

Chrome, however, still works great. Gives no problems with log-ins.

The "strange advertising posts" have always been there; cnczone gets paid to have for some strange reason to have OT posts that usually have nothing to do with CNC. Hard to believe it generates any click-throughs at all.

"Closed thread" announcements have showed up for me when not logged in for months, so I don't think that is anything new.

PIA.

[SCzEngrgGroup]

Chrome, however, still works great. Gives no problems with log-ins.

Chrome is massively hosed for me. Sadly, since the software "upgrade" a couple years ago, CNCZone has been, by FAR, the slowest, most troublesome and least reliable of all the forums I frequent. It's now been all but unusable for at least 5 days.

Regards,
Ray L.

[TurboStep]

Hey guys, this thread is about countersinking!
Please don't hijack it for unrelated ranting. It doesn't belong in this thread and is not very respectful to those discussing the original subject.
Thanks
Step

[RussMachine]

Sorry Step.
But this was the only 'open' thread that wasn't closed when the hacker/glitch problem occurred.
There weren't any tabs for 'new thread' at the time either.
Carry on with countersinking.