how to avoid tear out when routing?

[jonnyfontaine]

hi, almost everytime i use my router i use a template and a pattern bit... and in an attempt to aviod tear out i usually only cut about 2-3mms deep at a time and move the router pretty slowly, just fast enough so there is no burning, but yet i still get frequent tear out... i have pretty decent bits, that are sharp, i've tried adjusting the speed of the router motor but with no avail... especially when routing against the grain, there's a lot of tear out... is there a way to keep this to a minimum... i tried back routing which seems to help... are there other ways to combat this? thanks... jonny

 

[DaveO]

I just left you some tips in your other post. The key to avoiding tearout is watching which way the grain is going. That, and light cuts will help. When you said that "back routing" helped, that is climb cutting and has reversed your approach angle to the grain. But that needs to be done very carefully and with very light cuts or you can lose control of the router. I have been searching for someting that will try to explain what I am trying to say better, but to no avail. Hopefully someone can explain it better than me.
Dave

 

[striker]

you mite try moistening the routed area prior to routing and/or using a spiral bit.

Stephen

 

[Travis Porter]

What kind of bit are you using and cut are you trying to make?

 

[walnutjerry]

And what wood are you routing?

Jerry

 

[dave "dhi"]

back routing seems to do the job for me! :icon_thum

 

[Tarhead]

I use my oscillating spindle/belt sander and after bandsawing (or jig sawing) close to the line. Pattern router bits only give me consistently clean cuts in MDF.

 

[sapwood]

Woodworkers Journal has a good article on router bits and tear out this month. As I read it, a down cut bit is less likely to create tear out . . . at least on the top side of the piece your routing :eusa_thin And as others suggested, a climb cut can reduce tear out, but is difficult to control.

Roger

 

[Joe Scharle]

Back or climb cutting can be controlled if restricted to the last 1/8" or so. Just pull the work away before you reach the end and run the work in reverse for the last little bit. Practice with some scrap until you get the feel. And a sacrificial pusher block that is as tall as your bearing will help prevent tear-out too.

 

[DavidF]

I've been using shear cut bits recently and the tear out is much reduced. They even do a shear up/down bit down in soilid carbide that should help on both sides of the work.

 

[cpowell]

I have the same problem routing with templates on longer curved pieces. It just doesn't always work with standard bits. I screwed up an S-curve shaped cherry arm rail last night - chunked out in the curve. I had bandsawed around 1/16th - 3/32nd off the line and still failed. Admittedly, cherry is more prone to tearout than some other species.

I remade the piece, sawing to the line this time, and cleaned both arm rails with the stationary belt sander. The pieces are not identical but close enough that it will not be noticed.

I am interested in the responses. If a different bit would shear without demolition I would like to try one out.


Chuck

 

[sapwood]

According to Billy Hylton's article (not Roger's experience :eusa_whis) the best way to avoid tear out using template on hardwood is to use two router bits. You need to ensure your sweeping down on the grain where it runs out the edge. Cutting against the grain causes tear out/splitting. Therefore you do part of the curve with pattern bit, then turn the piece over and complete cut with flush trimmer bit.

Does that make sense? :eusa_doh: I'm a "bit" confused :-?

Roger

 

[Ray Martin]

In Roger's first response, he suggested a down cut spiral. That should help since you won't be pulling up against the top of the grain but rather shearing downwards. The drawback to this kind of bit is that the debris is not cleared very well and can cause heat to build up quickly. If you use a down cut spiral, you should make a couple of shallow cuts rather than hog all the material out for the full depth of the cut.

And sometimes... it's just the wood.

Ray

 

[Travis Porter]

I do have a carbide spiral flush trim bit that I got way back that does an excellent job compared to the regulars. Bad part is it was not cheap. IIRC, it was around $100 for it, but it is an extra long one that has 2" cutting length.

Working on the bench I have been using a very large (1" diameter) pattern cutting bit and I have been quite surprised at how cleanly it cuts. Maybe the larger diameter has something to do with cleaner cuts.

 

[jonnyfontaine]

hi, thanks for all the advice... i am using a straight pattern bit with honduras mahogany... i looked up some of those spiral bits, are there none of those bits with a bearing on the top for use with patterns... but i guess if the cutting dia. is the same as the shank, the shank could be used almost like a bearing... and i've heard that those bits are very fragile, how fragile? and how different would you need to use them? also i've seen this bits that instead of an up cut or down cut, they are i think compression spirals some sort of combination of the two, does anyone know much about these? also the shear cut bits, are those much better than just a regular 2 fluted straight cut bit? thanks again... for all the advice

 

[Tarhead]

Here are some options:
You'll need to put the pattern on the table and use an upcutting bit. I have seen a double bearing (top and bottom) spiral bit somewhere but it's not showing up anywhere.

Spiral,top bearing Pattern bits:
http://www.infinitytools.com/products.asp?dept=1339

http://www.infinitytools.com/products.asp?dept=1335

High end straight cutter set:

http://www.patwarner.com/straight_bit_kit.html

Lots of flush trim bits:
http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/bt_solid.html
http://www.mlcswoodworking.com/shop...html/pages/bt_flush.html#pattern_flush_anchor

Whiteside at WC:
http://www.woodcraft.com/family.aspx?familyid=8005&refcode=07INAFFL

http://www.carbide.com/catalog/RBits-SS-SC-flush-spiral.cfm

As far as fragility for what you're doing you should be ok. Just don't drop it or try to take big bites.