routing with template tearout

[Zed]

Hi Guys,

Some advice please - I am making a bench for my wife with some timber that Bodge gave me. I've done all the glue ups and now have made the template in MDF and cut the blanks to approx shape witha jig saw. when I double sided taped the template to the blanks and started using a roller bearing profile straight bit to guide to shape i got HORRENDIOUS chatter and blank destroying tear out - I was only taking off about 1MM at a time but still no good - I'll have to reglue a new blank now - quite peeved..

Question - how can this be avoided - cut the final profile with the jigsaw and sand to shape ? surely not.

ta

Zed

[ozwinner]

Hi Guys,

Some advice please - I am making a bench for my wife Zed


Cant you just find a Chimp to be your wife?
Sicko!!

Al :p

[Stuart]

No you shouldn't have to. I am struggling to understand (as you are I'm sure Zed!) how the hell you got that much trouble with only a 1mm pass.

Probably need a bit of clarification - table or handheld, free-running bearing (not stuck or anything), with the grain or crossgrain (or problem in both direction), sharp bit, correct feed direction (yeah, I know, shouldn't have to ask, but then the situation is pretty unusual). Speed fast enough?

Sheesh, none of these should have tripped you up though.... hard one mate.

[echnidna]

Keep making light cuts but push the router the other direction so you are climb cutting. You will get an erratic edge but with little or no tearout or chipping

The erratic edge is removed if you just keep going around the template until the full cut is finished.

[Stuart]

Just another thought - if you are only taking off a mm at a time, I'm guessing you didn't get that close to the line with your jigsaw, so is the bit unsupported against the template (ie - too far from the template during the pass for the bearing to contact it) So if there is chatter, it doesn't have anything to press against to resist a resonance occuring. (if that makes sense).

What you may want to do if that is the case, is replace the bearing with one of a wider diameter initially, so you can take off a narrow band of material while still keeping the bearing in contact with the template. After the first pass, you can go to a smaller bearing and do another pass, and repeat until you are running the final bearing that comes with the cutter.

[Auld Bassoon]

Have you checked the cutter? Taking a 1mm pass should be pretty straightforward - as well you would know. Seems very odd...

Are you using a hand-held router going clockwise, or in a table going right to left (sorry, very basic stuff!)?

[Bodgy]

THree things occur to me:

1. You are using a dull bit
2. You are cutting against the grain
3. The tape you are using is not holding the template to the work well enuff and its a bit loose, hence it chatters against the bit.

If u need a brand new bit, let me know, cause I just bought a big set of 1/2 assorts.

The one I wanted was about $50 in a 'quality' brand and a set of 15 was $50 inc the one I wanted.

[scooter]

Sounds like you're cutting against the grain. Try attaching the template to the other side of the wood; or using the opposite guided cutter to what you're currently using, ie if you're using a flush trim bit (bearing on the end), swap to a pattern bit (bearing on the shaft).


Good luck..........cheers..........Sean

[Zed]

good work guys - cuttiong in every grain direction (its a complex curved shape - willpost finished pic) ... had another look at the bit its real long and not quite straight! basturd!! ok - new bit, new blank, smaller lighter cuts, faster turning bit, wider bearing. gotcha!

[Zed]

PS Bodge - thanks for the offer but I think I will buy a new bigger diameter profile bit with the interchangable rollers in lotsa sizes (the one im using is only 12mm) - im gunna need one anyway so may as well get a new one rather than sponge off you for a commonly used bit :p

PS 2 - hand held around a template approx 900 x 650mm in a complex curve shape - like a h in "Book antiqua" font (as shown left..)

[Wongo]

Zed what bit do you use? A $40 CMT bit or one of those 30 bits for $40 bit?

[Cliff Rogers]

I have a nice bench top template if you are interested. ;)

Maybe not. :p

[Harry72]

Sounds like a job for a spiral bit!

[Stuart]

PS Bodge - thanks for the offer but I think I will buy a new bigger diameter profile bit with the interchangable rollers in lotsa sizes (the one im using is only 12mm)

The linbide roller pack from Woodworking Warehouse comes under their 50% off offer fwiw....... Just thought I'd mention it, because from experience, those packs of rollers for router bits are bloody expensive.

[silentC]

When you are going around a shape like that, you are always going to end up cutting in the wrong direction if you just go around clockwise. When you get to the end grain, the cutter is revolving in a direction that wants to pick it up and throw it across the room, which is where you get tearout. You need to do a climb cut on those corners so that you sneak up on it from the other direction. It can still be a bit hairy, so very fine cuts <1mm and a sharp cutter, Zeddy boy.

[Stuart]

And one that isn't bent!

[Zed]

whats climb cutting ? is that a fancy name for a spiral bit technique ?

PS - the bent one is already been de-ball bearinged and tossed - mungrel thing!

[silentC]

Ah, but did the bend cause the bang, or did the bang cause the bend? ;)

[Zed]

the bend was "previous" ... so much for straight profile cutting!

[silentC]

Climb cutting is where you go in the opposite direction to the normal feed direction. You go in the direction of the bit rotation. Normally you push against the rotation. The resistance is against the direction you are pushing and the rotation of the bit holds the work tight against the fence (the bearing). With a climb cut you go the other way. The cutter wants to push the work away from the fence and it wants to grab it and fling it across the room. It reduces tearout because the blade is entering at the face of the cut, rather than exiting, where it wants to tear fibres out as it goes.

[Wongo]

It has been bothering me all morning.:D

If you have a sharp bit, a high speed router, slow feed rate and you only take 1mm off at a time. You should get a perfect cut whether it is with the grain or against the grain.

[silentC]

Not necessarily. That's why we have a name for the climb cut...

It's simple physics. When you get to the edge, there are fibres parallel to the edge on the outside of the wood. The blade attempts to cut through them but instead it flicks them out because there are no fibres on the other side to hold them in place. They break (usually, sometimes they don't and you get a fuzzy edge instead) and you have tear out. It depends on which direction you approach them from as to whether or not that happens. When you are routing around the full perimeter of a board, it is inevitable that you will arrive at this situation. What happens next is subject to a lot of variables, but very often it is tear out time.

Also, sometimes slow feed is not good because it can cause burning.

[Wongo]

Understood. You have already mentioned it in one of your previous posts.

How slow is too slow?

[silentC]

2" or 3" per second is about right ;)

[Wongo]

Exactly!

[Stuart]

Understood. You have already mentioned it in one of your previous posts.

How slow is too slow?when you see whisps of smoke, or flames :D (or when you turn out the light, the router bit is still glowing ;) )

[Harry72]

Zed grab yourself a spiral bit, this is the kind of job they excel at. Its because of the sharp shear angle they have, the wood fibers are sliced instead of chopped/scooped action of a normal bit.
They leave an almost polished finish on ply wood, plus there's no need to risk your safety with climb cutting.

[John Saxton]

Zed one question ,what was the nature of the grain when the tear-out occurred?
Sometimes when "wild Grain" is present and often around areas in wood where branche's/limbs were present can be a problem and this is where SILENT has hit the nail on the head in employing a 'climbing' cut.

If in doubt the climbing cut will often get you thru a difficult cut as I have found with m/c cut dovetails in some hardwoods.

Also Harry has put you in the picture on having a spiral bit handy should you not be comfortable in using the climbing cut technique...it requires one to brace oneslf against the throw of the router...best to try some practice runs on scrap to get the feel of how the router reacts to your stance.

The climbing cut is only problematic if you dont take a firm hold and control of the router..remember you're pushing against the natural direction of the router.

Cheers HTH :)

[Template Tom]

Zed
I have read through all the postings and no where was there any mention of the thickness of your material. If it is thick I could offer an alternative solution to your problem.
Tom

[Zed]

Tom the material is:

blackbutt
38mm thick
all grain directions
well seasonedI thnk i'll get a spiral cutter with some bearings.

ta all.

[silentC]

I thnk i'll get a spiral cutter with some bearings.
Is there such a beast? I've never seen one...

[Wongo]

Carbatec has them but I heard that they are not very good.

[Bodgy]

You can go to any of the bearing places, eg CBC and get a ball race for any bit, Most of the guys are very helpful, take your bit in with you and they'll fit the bearing.

Cost = a few dollars.

[silentC]

Still llooking, haven't found one yet.

Actually, spiral bits are designed for plunge cutting, not edges. The shape is designed to pull the waste up out of the groove so that it doesn't clog. There are also down cut bits but I've never worked out what they're for :confused:

[silentC]

You can go to any of the bearing places, eg CBC and get a ball race for any bit
Yeah but it needs to have a tapped hole in the top. Spiral cutters are usually end mills too.

[silentC]

Carbatec has them but I heard that they are not very good.
Ah, found them. Well roger me with a bargepole :p

[Wongo]

how Bodgy?

[zelk]

Zed, assuming the bit is OK, if it's possible, don't cut the full thickness, start with, let's say, one third depth and then increase the depth with each new pass, usually you require to either vary the height of the template or use two different length template cutters.
Zelk

[silentC]

That wont work with that spiral cutter with the bearing because it's a bottom bearing, not top. The length of the shaft has to go past the full thickness of the wood being cut to get to the template. With a top bearing bit, you could do it, but it would be difficult because the template is usually only thin, around 5mm.

[zelk]

That wont work with that spiral cutter with the bearing because it's a bottom bearing, not top. The length of the shaft has to go past the full thickness of the wood being cut to get to the template. With a top bearing bit, you could do it, but it would be difficult because the template is usually only thin, around 5mm.
silentC, I had in mind a straight cutter with the bearing above.
Zelk

[silentC]

Yep realise that. I'm just saying it wont work with the bit that Zed is proposing to buy. He'd have to buy a pattern following bit with the bearing above as you say.

[chrisp]

Still llooking, haven't found one yet.

There are also down cut bits but I've never worked out what they're for :confused:

silent,

Spiral downcut bits are good for inlay work - they leave a nice sharp edge. Upcut bits can leave a fluffy (technical term? :o ) edge.

Downcut are also good for edge trimming as well - they leave a very clean top edge. There are also spiral up- and down-cutter that cuts towards the centre of the bit. (The top part is a downcutter and the bottom part is an upcutter). These are edge trimming bits that leave a very clean top and bottom but I haven't tried them.

[Template Tom]

Zed
You have to consider an alternative method and use the Plunge method using a 4-5mm cut at anytime
Tom

[schaf]

Template Tom ,good to hear from you.
Terry

[Harry72]

Silent, he wouldnt use a bearing on the spiral bit instead you'd use a template guide and make the temple accordingly to size.

[Template Tom]

Tom the material is:

blackbutt
38mm thick
all grain directions
well seasonedI thnk i'll get a spiral cutter with some bearings.

ta all.

Is there any chance that you could post a pic of what you are trying to do The shape of the cut-out and size
Tom