Burnt bits - Router Forums
 7Likes
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 21 (permalink) Old 07-26-2015, 03:55 AM Thread Starter
Registered User
 
Join Date: Jul 2015
Country: France
First Name: Mark
Posts: 13
 
Default Burnt bits

Look at the state of these two 1/4in bits (see upload). These are best-quality bits made long ago by Trend in the UK, and both were professionally sharpened in the past year. But today as always, I find they blacken up like no other bits I use (including Chinese). I think I must be doing something wrong with them. What is it? I use them almost exclusively to cut natural wood - mainly these days, adjustment slots in jigs. I run them at or close to the router's maximum speed. I plunge my cuts by sensible degrees. And yet ... There's the 'coffee grinder' effect of chips trapped in a narrow slot. Nasty smell of burning. Is that it, and is it actually unavoidable? Or is there some lick that I have been missing these past 30 years? Any advice gratefully received.

Cheers
Mark
Attached Thumbnails
Click image for larger version

Name:	DSCF7308.jpg
Views:	587
Size:	803.7 KB
ID:	135514  

guardoff is offline  
Sponsored Links
Advertisement
 
post #2 of 21 (permalink) Old 07-26-2015, 09:53 AM
Forum Contributor
 
Stick486's Avatar
 
Join Date: Jan 2013
Country: United States
First Name: Stick
Posts: 25,113
 
Default

incorrectly sharpened...
any other bits doing that???
mbar57 likes this.

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
Stick486 is online now  
post #3 of 21 (permalink) Old 07-26-2015, 10:37 AM
Retired Moderator
 
Mike's Avatar
 
Join Date: Nov 2004
Country: United States
First Name: Mike
Posts: 11,921
 
Send a message via Skype™ to Mike
Default

Mark, the bits are getting too hot. I agree with Stick that this is most likely caused by not being sharpened properly. Once the bit has changed color like that you have lost the temper of the HSS.

I use a couple of Trend products that I think you could make good use of: their diamond card sharpener and their Tool and Bit cleaner. Both products work very well and I will post a thread tonight showing how to touch up a bit.
mbar57 likes this.

Mike
"Living in the D" (this means Detroit!)
"It's fine to disagree with other members as long as you respect their opinions"
Mike is offline  
Sponsored Links
Advertisement
 
post #4 of 21 (permalink) Old 07-26-2015, 10:51 AM
Forum Contributor
 
Stick486's Avatar
 
Join Date: Jan 2013
Country: United States
First Name: Stick
Posts: 25,113
 
Default

@Mike ...
those look to be carbide bits..
pretty sure any ways...
Attached Files
File Type: pdf Care and Sharpening of Router Bits.pdf (123.5 KB, 191 views)
File Type: pdf ROUTER SPEEDS-BURNING.pdf (212.1 KB, 207 views)
firstmuller and mbar57 like this.

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
Stick486 is online now  
post #5 of 21 (permalink) Old 07-26-2015, 10:59 AM
Moderation Team
 
Cherryville Chuck's Avatar
 
Join Date: Sep 2010
Country: Canada
First Name: Charles
Posts: 14,965
 
Default

Is the wood you are using very pitchy? Resin buildup will slow the chips from clearing the cutting edge like they should and would generate heat.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
Cherryville Chuck is offline  
post #6 of 21 (permalink) Old 07-26-2015, 11:23 AM
Registered User
 
Ghidrah's Avatar
 
Join Date: Oct 2008
Country: United States
First Name: Ronald
Posts: 1,466
 
Default

guardoff,

When ever I had a bit get too hot, it went to a yellowish/purplish/blue never black. The black I found on my bits was from the wood being heated to char then smearing on the outer surface of the bit. Also the bluing or charring occurred only at the point of contact; nearly the entire length of both bits is discolored in the pic.

Those aren't plunge bits; they don't have the plunge bit crossbar between the carbide tips that would clear out debris before it could burn. Wood binds up in the hollow between the carbide, heats and burns.

Plunging a non plunging bit requires the router to be moving as the bit is lowered into the cut.
Is it possible the bits or wood has come in contact with something?
Did the bits burn before the 1st resharpening?
Have you tried a 3rd bit, diff brand and duped the process to see if it burns?

Never bite the hand that looks dirty!
The more you know the more you're worth
Ghidrah is offline  
post #7 of 21 (permalink) Old 07-26-2015, 11:45 AM
Retired Moderator
 
Mike's Avatar
 
Join Date: Nov 2004
Country: United States
First Name: Mike
Posts: 11,921
 
Send a message via Skype™ to Mike
Default

Yes Stick, I was trying to make a point. Some times you just can't short cut an explanation; my bad. Tool steel has lost its temper when it changes color like that. For a carbide tipped bit to overheat and change color like that it has been improperly ground when sharpened. There is not enough relief behind the carbide and the wood is hitting the steel of the bit or the cutting angle is ground wrong which has the same effect. My guess is that when the bit was sharpened it was ground on the outside surface to restore a sharp cutting edge. It is acting as a scraper instead of cutting. It is easy to verify this by checking the actual diameter across the cutting edges. If it is smaller than what it is supposed to be by a fair margin this is what happened. Every time a bit is properly sharpened it will lose a tiny amount of diameter which will not effect performance and this will be in thousandths of an inch. Incorrectly sharpened bits will be reduced by hundredths of an inch. If the shear angle of a carbide tipped bit is altered it will result in friction and heat.

I bought one cheap bit that had too thick of a paint coating on it which caused instant burning of the wood and tremendous heat on the bit. I took it back for a refund.

Trend's Tool and Bit cleaner does a great job of removing resins and rust; it also lubricates the bit. Any build up on a bit will result in heat being generated so this is an easy way to avoid that happening. Priced here at $12 a bottle it is cheap insurance. 20 minutes with Tool and Bit cleaner salvaged these bits I got in a package deal.
Attached Thumbnails
Click image for larger version

Name:	Rusty bits 01.JPG
Views:	202
Size:	34.9 KB
ID:	135601  

Click image for larger version

Name:	Rusty bits 02.JPG
Views:	173
Size:	53.3 KB
ID:	135609  

Attached Images
 
neville9999 likes this.

Mike
"Living in the D" (this means Detroit!)
"It's fine to disagree with other members as long as you respect their opinions"
Mike is offline  
post #8 of 21 (permalink) Old 07-26-2015, 12:05 PM Thread Starter
Registered User
 
Join Date: Jul 2015
Country: France
First Name: Mark
Posts: 13
 
Default

Thanks to you all. Mike, I look forward to your post about touching up a bit. Stick, those are two-flute bits with TC cutters. Ghidrah, you say these are not plunge bits, and that does surprise me. Fact is, I am only raising the issue after all these years because this forum gives me the opportunity to do so. The biggest issue, I think, is the quality of the bits' recent professional sharpening (which was their first sharpening ever). So I will slap the work down on their counter when I am next in the shop and demand an explanation. They are nice people and will surely have something intelligent to say. Which I will report back to you, and you can all tell me how wrong they are.

To be continued
Mark
guardoff is offline  
post #9 of 21 (permalink) Old 07-26-2015, 02:40 PM
Registered User
 
Ghidrah's Avatar
 
Join Date: Oct 2008
Country: United States
First Name: Ronald
Posts: 1,466
 
Default

gaurdoff,

As Mike and Stick pointed out likely bad bit sharpening.
Still I've never seen a bit, let alone 2 side-by-side with nearly identical scorching for most of the length of the bit including the shank.
It's bugging the crap out of me, at what point in the process did the smell of hot metal, burning wood, the sound of a strained router or the visible burned results in the cut area were you prompted to stop and question?

Never bite the hand that looks dirty!
The more you know the more you're worth
Ghidrah is offline  
post #10 of 21 (permalink) Old 07-26-2015, 03:01 PM
Retired Moderator
 
Mike's Avatar
 
Join Date: Nov 2004
Country: United States
First Name: Mike
Posts: 11,921
 
Send a message via Skype™ to Mike
Default

Ron, this sort of overheating happens without notice. No way to tell until you stop the bit. The cut can even look normal.

Mike
"Living in the D" (this means Detroit!)
"It's fine to disagree with other members as long as you respect their opinions"
Mike is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Router Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
Need advice on aquiring bits Goldstar225 Router Bits - Types and Usage 8 03-15-2015 04:28 PM
Getting started with router bits Mike Router Bits - Types and Usage 26 02-22-2015 03:23 PM
Metric and Imperial Routing Bits awhitecat General Routing 17 11-28-2014 07:10 PM
Need advice CNC End mills Vs. router bits SubmarineGuy CNC Routing 8 11-17-2014 08:59 AM

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

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome