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Pattern Bit Chipout - Need Advice

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Forum topic by becikeja posted 01-22-2017 10:47 PM 718 views 0 times favorited 16 replies Add to Favorites Watch
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becikeja

947 posts in 3013 days


01-22-2017 10:47 PM

Today is the first time I have ever tried using a trim bit. It did not go so well.
Yesterday I made patterns for a small rocking horse out of 1/4” birch plywood.
Today I rough cut pieces of 1” Mahogany and attempted to use the trim bit to guide around the patterns.
Some pieces came out perfect and others had major chipping. At one point the bearing retaining screw came flying out of the bit.

I’m not sure if it was the wrong bit, or my technique. Is there a different bit I should be using to avoid chipping?

-- Don't outsmart your common sense


16 replies so far

View Bill White's profile

Bill White

5124 posts in 4161 days


#1 posted 01-22-2017 11:01 PM

Taking too big of a cut, cutting against the grain, what speed?
Bill

-- bill@magraphics.us

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becikeja

947 posts in 3013 days


#2 posted 01-22-2017 11:18 PM

The cut was less than 1/8”, speed I am not sure I have a Bosch 1617EVS and had it close to high speed.
I am sure in some places around the pattern it went against the grain, but that would have been the same on every piece wouldn’t it?

-- Don't outsmart your common sense

View waho6o9's profile

waho6o9

8519 posts in 2777 days


#3 posted 01-22-2017 11:21 PM

They make bits with one bearing as well.

Here’s some other ones:

View Dale J Struhar Sr's profile

Dale J Struhar Sr

497 posts in 3331 days


#4 posted 01-23-2017 12:17 AM

Spiral bits work best. Cost more but work better.

-- Dale, Ohio

View JBrow's profile

JBrow

1366 posts in 1120 days


#5 posted 01-23-2017 01:31 AM

Becikeja,

In addition to what has been said about light passes and using a compression router bit, a little back routing might be required, assuming the finished piece is curved. Back routing is helpful with the type of flush trim bit shown in your photo. I am not sure that back routing is necessary with the compression bit, since I do not have a compression bit.

On a curved work piece roughed out at the bandsaw, the grain changes direction where the curve changes direction. When routing against the rotation of the router bit, things go well up to the top of the curve. After that, the router bit can grab the ends of the wood fibers and cause tear out.

Where this problem exists, back routing the problematic portion of the curve dramatically reduces tear out. I like to back rout a curved segment first and then rout the entire workpiece in the normal direction of travel. This final pass cleans up the slight bumps that can sometimes be left by the back routing (from the router pushing away from the cut). Very light passes are required when back routing to keep the router under control and help avoid it from pushing away from the cut. A firm grip on the router helps also.

By the way, I too have had a screw loosen on a flush trim bit the first time I used it. Your experience confirms that the router bit makers do not seem to always lock those tiny screws down tight. I now check the tightness of the bearing screw before routing.

View Rich's profile

Rich

3880 posts in 790 days


#6 posted 01-23-2017 01:43 AM

Those Whiteside compression bits are a thing of beauty, but at around $175 apiece, a bit pricey.

I’d recommend a combination bit to the OP. Trim bits going “upgrain” have the same issues as jointing and plaining against grain sloping up towards you. A combination bit has a bearing at the top and bottom of the bit so that you can flip your piece with the pattern attached and raise or lower the bit to ride against the pattern regardless of whether it’s on the top or bottom of the piece you are trimming. It allows you to always be cutting along the grain in such a way that you don’t lift it and get tear out.

Some operations like rounding endgrain against the grain are downright dangerous and can cause severe kickback. Again, a combination bit allows you to always be cutting with the grain.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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EricTwice

246 posts in 734 days


#7 posted 01-23-2017 02:08 AM

I usually make my patterns from 9 ply 1/2 inch. I find it works better. rough things out with a band saw to about 3/32 over size. If I am cutting against the grain I will back the router through and then cut forward.

and when I’m done will go back and fill the tear out. Sometimes, it’s just the nature of the beast.

-- nice recovery, They should pay extra for that mistake, Eric E.

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Tony_S

955 posts in 3283 days


#8 posted 01-23-2017 11:03 AM



Those Whiteside compression bits are a thing of beauty, but at around $175 apiece, a bit pricey.

I brought a couple into the shop about a year ago. Actually, one compression, and one down shear. These bits are extremely impressive, and I’m not easily impressed. Worth every penny if you use FT bits regularly. Cut quality and edge retention is top notch.


I d recommend a combination bit to the OP. Trim bits going “upgrain” have the same issues as jointing and plaining against grain sloping up towards you. A combination bit has a bearing at the top and bottom of the bit so that you can flip your piece with the pattern attached and raise or lower the bit to ride against the pattern regardless of whether it s on the top or bottom of the piece you are trimming. It allows you to always be cutting along the grain in such a way that you don t lift it and get tear out.

Some operations like rounding endgrain against the grain are downright dangerous and can cause severe kickback. Again, a combination bit allows you to always be cutting with the grain.

- RichTaylor


100% This^


and when I m done will go back and fill the tear out. Sometimes, it s just the nature of the beast.
- EricTwice

Tame the beast. The wood beast should never win.

-- It is the mark of an educated mind to be able to entertain a thought without accepting it. Aristotle

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Rich

3880 posts in 790 days


#9 posted 01-23-2017 02:53 PM



The wood beast should never win.

- Tony_S

Awesome! I’m tempted to have a sign made with that and hang it in my shop. If I do, before I hang it, I’ll ship it to you for your autograph.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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becikeja

947 posts in 3013 days


#10 posted 01-24-2017 03:46 AM

The spiral bits seem interesting, I’ll look into these. I have the bit mounted in a router table, would you use up-cut or down-cut, or do you have to go with the compression. The compression bits are pretty high dollar.

JBrow – thanks for the picture, I think this is exactly what happened.

-- Don't outsmart your common sense

View pintodeluxe's profile

pintodeluxe

5798 posts in 3014 days


#11 posted 01-24-2017 04:51 AM

If you can get the cut closer to 1/16” from the line, even the straight bits should cut cleanly.

Was it a new bit? A sharp bit makes all the difference. Sharp and dull bits look and feel almost the same.

Once in a while I will just sand curves on the oscillating belt sander. It eliminates tearout entirely, and costs about the same as those spiral router bits.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View Loren's profile

Loren

10477 posts in 3848 days


#12 posted 01-24-2017 04:55 AM

climb cutting.

A pin router with a spiral bit does a pretty good
job on pattern cutouts, but you can’t put a
bearing on a spiral bit as far as I know.

Another solution is to use stepped depth cuts
using a template guide.

I use a pin router but I still use stepped cuts

You can of course acquire pattern bits with
the bearing on top in different depths.

I feel the simplest solution is the template
guide bushing/spiral bit approach. You’ll have
to make new patterns but the final results will
be better.

about 1/8” in depth increments and climb cutting
when the grain goes against you.

View Rich's profile

Rich

3880 posts in 790 days


#13 posted 01-24-2017 05:35 AM


about 1/8” in depth increments and climb cutting
when the grain goes against you.

- Loren

Using my Amana trim bit, I tried everything to eliminate kick back. I wanted badly to avoid having to buy a combination bit. I was trimming some glued-up stacks of 1/2” baltic birch for a sled fence.

I did the usual cut up-grain, and the piece shot across the room. I thought, sure, climb cut. No friggin’ way. I do not care what direction you are coming from, it will grab and give you a nasty kick back.

Get a combination bit. Period.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View JBrow's profile

JBrow

1366 posts in 1120 days


#14 posted 01-24-2017 12:33 PM

Becikeja,

It is my belief, evidently confirmed by TonyS’s experience, that the likelihood of tear out is reduced on both faces adjoining a routed edge with a compression bit. I believe the compression bit shears wood fibers on both the upper and lower faces of the stock in both an up and down directions. Up cut and down cut router bits produce an upward or downward shearing action and thus tear out could occur on one surface, the surface where the shearing action is directed away from the face. If mounted in a router table, the up cut bit will direct chips downward under the router table.

There is another style of straight bit not mentioned where the cutting edge is skewed or angled relative to the router bit shank. Thus, this bit also cuts with a shearing action and could reduce tear out along one face that abuts the routed edge but not the other face. Since only the edge is carbide and I suspect it is cheaper to manufacturer, this bit costs less than the solid carbide up cut, down cut, and compression bits. However, I do not recall seeing a shearing straight bit equipped with a bearing, but then I have not done an exhaustive search.

View OSB's profile

OSB

147 posts in 726 days


#15 posted 01-24-2017 04:40 PM

Those bearings suck. I’m not sure about that combination bit either, if it is 1/2” shank, the cut will have to be something like 7/8” to fit the top bearing. If it is 1/4” shank, you can bend the shank pretty easily and once that happens it is garbage.

I have used bushings to guide a router but you need a precisely undersized template to make that work.

You can get a spiral bit a lot cheaper if you don’t need a bearing and since bearings suck, a pin router is the best solution for manual router copying.

There are some simple pin router versions that suspend a pin over a router table, easy to DIY, there are hobby size overarm routers and there are the real deal production style that are being replaced by CNC machines.

Overarm has the advantage that the template rides on the table so your workpiece does not get dragged over it but otherwise they have similar capabilities.

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