VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #1  
Old 02-24-2018, 06:57 PM
asw20c asw20c is offline
 
Join Date: Jun 2010
Location: Edgewood, NM
Posts: 140
Default Countersink Scratches

I tend to get these weird scratches on the aluminum when countersinking. It obviously can't be the bit, and the location puts the scratches somewhere between the bit and the cage. The only thing I can figure what is causing it is probably the chips coming out of the hole somehow get swept around the countersink between the bit and cage. I would expect to see concentric circles, which are there, but the irregularly shaped scratch is the real mystery. Is my technique messed up somehow? Does anyone have any insight into how or why this is happening?
__________________
Empennage Complete Except for Tips
Wings Underway
Reply With Quote
  #2  
Old 02-24-2018, 07:09 PM
asw20c asw20c is offline
 
Join Date: Jun 2010
Location: Edgewood, NM
Posts: 140
Default

__________________
Empennage Complete Except for Tips
Wings Underway

Last edited by asw20c : 02-24-2018 at 07:13 PM.
Reply With Quote
  #3  
Old 02-24-2018, 07:15 PM
vernon smith's Avatar
vernon smith vernon smith is offline
 
Join Date: Jun 2017
Location: Naples FL
Posts: 140
Default

These came from the countersink depth guard spinning against the work. Either hold onto the guard with one hand so it doesn't spin or buy the adjustable countersinks sold by Pan American Tool;

http://www.panamericantool.com/count...e-bearing.html

They have a Teflon protective ring around the surface that contacts the work preventing the guard from spinning and from scratching the work.
Reply With Quote
  #4  
Old 02-24-2018, 07:24 PM
asw20c asw20c is offline
 
Join Date: Jun 2010
Location: Edgewood, NM
Posts: 140
Default

Nope. My countersink cage has the nylon lip that contacts the work and it wasn't spinning. If you look closely at the photo you will see what looks like a dusty ring. That ring is where the nylon lip contacted the work and it is outside the scratches.
__________________
Empennage Complete Except for Tips
Wings Underway
Reply With Quote
  #5  
Old 02-24-2018, 07:36 PM
VA Maule VA Maule is offline
 
Join Date: Apr 2016
Location: Bucking ham, Virginia
Posts: 108
Default

I don't think it's the depth guard,the scrap is the same size as the Cleco to the right. Looks to me that you're applying too much pressure at the start and making too large chips and curls coming off the bit faster than they can exit and subsequently they drag around in the cage making the scratches.
__________________
The Best Government is less Government
Maule MXT-7(daily flyer)
Lancer 235(partner)
Raidial RV-8R Ephanage Done, Wings Done, Fuselage underway
Reply With Quote
  #6  
Old 02-25-2018, 08:06 AM
asw20c asw20c is offline
 
Join Date: Jun 2010
Location: Edgewood, NM
Posts: 140
Default

Thanks. I thought it might be a technique problem. I'll try it without so much pressure next time.
__________________
Empennage Complete Except for Tips
Wings Underway
Reply With Quote
  #7  
Old 02-25-2018, 09:20 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 7,555
Default

Using an air drill running at high speed can also be a factor in scratches caused by swarf (chips).
Slower speed and medium pressure also reduces the chance of cutter chatter.
__________________
Any opinions expressed in this message are my own and not necessarily those of my employer.

Scott McDaniels
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
Reply With Quote
  #8  
Old 02-25-2018, 11:38 AM
XOverZero's Avatar
XOverZero XOverZero is offline
 
Join Date: Aug 2010
Location: Irvine, CA
Posts: 390
Default

I had several instances of concentric scratches at countersinks. It was caused by my using a single flute bit in the cs cage. One flute creates one long continuous chip that bunches up and spins with the cutter. I switched to a multi flute cutter. No more swirlies. Short chips just fly out and away.
__________________
John Halcrow
Irvine, CA
RV-12 120682
Emp/TC done; Wings done; Fuse kit done

"History teaches us that men and nations behave wisely once they have exhausted all other alternatives." --Abba Eban
Paid up until Aug 2018
Reply With Quote
  #9  
Old 02-25-2018, 11:44 AM
StressedOut StressedOut is offline
 
Join Date: Jun 2017
Location: Fullerton, CA
Posts: 71
Default

I had terrible problems with massive chatter the first time I tried to countersink. It was on the VS doubler which is 0.125 thick. Besides screeching like a banshee, I got small aluminum particles and the characteristic wavy looking surface.

The only way I could solve the problem was by going very slow (about 120 rpm) and using very light pressure. Only then did I start getting smooth cuts and the long, curly chips. The resulting finish was superb as if it was polished.

I was using a three flute cutter from Cleaveland Tools. I also bought a single flute cutter, but before it arrived I solved my countersinking problems so I've never had a chance to use it.
__________________
Art Jackson
RV-14A Kit#140433
Completed: Vertical Stab
Scrapped: Rudder
Working on: Empennage (HS/Elevator)
Construction log - mykitlog.com/ajackson
Dues paid on 2 November 2017
Member of EAA Chapter 92 (KCNO)
Reply With Quote
  #10  
Old 02-25-2018, 04:27 PM
asw20c asw20c is offline
 
Join Date: Jun 2010
Location: Edgewood, NM
Posts: 140
Default

Here's another clue that may contribute to the conversation. This is a multi-flute countersink bit, and sometimes the chip bunches up like a tumbleweed and sticks to the bit. Usually I can just blow in the cage to clear out any chips, but sometimes I have to "dig" it out with something like a punch. In other words, it seems to be snagged, or stuck on the bit somehow and I have to break it up to get it out. This must be how those weird scratches are created, but again I would expect concentric circles and not the meandering scratch like in the photo.
__________________
Empennage Complete Except for Tips
Wings Underway
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 09:55 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.