Need help picking a flush trim bit

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Forum topic by BenI posted 12-07-2012 12:24 AM 9970 views 0 times favorited 20 replies Add to Favorites Watch
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333 posts in 3100 days

12-07-2012 12:24 AM

Topic tags/keywords: flush trim router spiral straight

Hi all,

I’m interested in getting a flush trim bit for a project in the near future and of course for others down the road. The problem is, even after some research I don’t really understand which type of flush trim bit would be best overall. Straight bits are cheaper but seem to have some tearout sometimes. Spiral bits make a smoother cut with less tear out but cost more. I’m leaning towards a spiral bit because you don’t really have to worry about grain direction as much (correct me if I’m wrong).

I’d like to know what others opinions are on this for overall performance, best results, etc.

By the way, I will be using this bit for templates to produce identical parts, and just for wood removal for now. If you need more info just ask me.

Thanks in advance LJ’s.

-- Ben from IL

20 replies so far

View HorizontalMike's profile


7904 posts in 3836 days

#1 posted 12-07-2012 12:30 AM

AFAIK, all flush trim bits are straight bits. That said, you should still be able to flush trim straight edges with a a variety of bits if you set up your fence properly.

-- HorizontalMike -- "Woodpeckers understand..."

View BenI's profile


333 posts in 3100 days

#2 posted 12-07-2012 01:19 AM

I think they’re newer but there are spiral bits for flush trim work and come as up cut or down cut and it seems they both have drawbacks.

Probably should have mentioned, the next project with involve a fair amount of flush trimming across the grain because it’ll have some sweeping curves.

-- Ben from IL

View BentheViking's profile


1782 posts in 3486 days

#3 posted 12-07-2012 01:53 AM

Go with something long or if you have the budget go with several sizes. First bit I bought when i got a big router was a 2” flush trim that way I can flush things of just about any height I probably need specifically thinking of being able to work on 2x stock

-- It's made of wood. Real sturdy.--Chubbs Peterson

View BenI's profile


333 posts in 3100 days

#4 posted 12-07-2012 06:48 AM

The only router I have is 1/4” shank so my options are somewhat limited but I am planning on getting one with a 1” cutting length which seems to be the limit for that size shank.

Anyone have any advice/comments/suggestions about straight vs. spiral flush trim bits??

-- Ben from IL

View Loren's profile


10804 posts in 4570 days

#5 posted 12-07-2012 06:57 AM

If you’re trimming laminate or other thin material get
something inexpensive and give it a go.

If you are looking to pattern route hardwoods,
especially over 3/4” thick… well, be prepared
to lose some hair figuring out how to get clean
cuts with a flush trim bit.

With router at 20,000 rpm give or take, if doing
pattern routing a pin router setup is the
best option. If working with a bearing my opinion
is a bigger diameter bit makes better cuts.

View Tony_S's profile


1362 posts in 4005 days

#6 posted 12-07-2012 11:53 AM

Spiral tooling 101 (in my experience)

What I’ve learned over the years talking to sales reps and running the tooling, both hand held and CNC. (flush trim, upshear, downshear, compression)

‘Out of the box’, spiral can’t be beat. The quality of the cut, particularly on end grain and other difficult to cut materials can’t even be compared to other styles of tooling.
Spirals are made of a higher grade of carbide and have a far sharper edge than more ‘standard’ types of router bits. That, in combination with the spiral design (which cuts like a knife rather than shears) makes the quality of the cut far superior.
Due to the higher grade carbide, they also stay sharper, longer. Rough estimate IME, 100 to 150% longer depending on material.

Expensive…easily twice the price, sometimes 3X.
Usually more costly to sharpen.
A combination of two other drawbacks also. Due to the geometry of the spiral bits and the fact most outfits can only ‘face grind’ them, they aren’t as sharp as new after the first sharpening, and even less so the second time.
Typically don’t get more than three sharpeinings max before they’re kaput.

All said…expensive to run. But worth every penny due to the end quality of the product. (IMO)

-- “Wise men speak because they have something to say; fools because they have to say something.” – Plato

View OggieOglethorpe's profile


1276 posts in 3032 days

#7 posted 12-07-2012 12:30 PM

My favorite way to flush trim is to attach the pattern, then bandsaw to ~ 1/16” to 1/18” from the pattern. I then make the first cut with either a few layers of tape or heat shrink tubing on the bearing. I then remove the “spacer” and carefully “climb cut” (backwards) the final pass.

If you’ve never climb cut, I suggest practicing on something you don’t care about, and be fully aware that much more than a thirty second of an inch cut may make the tool difficult to control and dangerous.

Spiral bits seem to be easier to control, grabbing less than straight bladed bits. Spirals are available with combination up and down, compression, cuts that leave two perfect edges. Bring money, but they work GREAT for cuts that really count.

View HorizontalMike's profile


7904 posts in 3836 days

#8 posted 12-07-2012 12:35 PM

Wow, I just learned something new again. I did not know that flush trim router bits can come in up/down spiral cut. Very interesting for this 3yr ww’r. However, I don’t think I could handle that $100 price tag though. 8-(

Freud 75-509 Flush Trim Upcut Spiral Solid Carbide Router Bit 1/2” Diameter 1/2” Shank With TiCo Hi-Density Carbide by Freud
5.0 out of 5 stars See all reviews (1 customer review) | Like (0)
List Price: $166.19
Price: $99.32 & this item ships for FREE with Super Saver Shipping. Details
You Save: $66.87 (40%)

-- HorizontalMike -- "Woodpeckers understand..."

View HorizontalMike's profile


7904 posts in 3836 days

#9 posted 12-07-2012 12:39 PM

10-4 on what Barry says about climb-cuts. I learned the hard way when my horizontal mortising machine took a piece, grabbed it and threw it across the shop. The piece looked like it had tank tracks down the length of it as the flat bit dug into the wood. This definitely made ME aware of routing in the correct direction.

-- HorizontalMike -- "Woodpeckers understand..."

View NiteWalker's profile


2741 posts in 3499 days

#10 posted 12-07-2012 12:45 PM

My go-to flush trim bits are whiteside downshear bits. Never any issues, just keep them clean. #2602 is the one you want.

I’ve done what barry suggest with success. The key is rough trimming as close to the line as you can without going over. The more waste trimmed away, the cleaner the cut.

-- He who dies with the most tools... dies with the emptiest wallet.

View kizerpea's profile


775 posts in 3290 days

#11 posted 12-07-2012 01:59 PM

+1 wid nitewalker


View BenI's profile


333 posts in 3100 days

#12 posted 12-07-2012 02:22 PM

Thank you soooo much for the responses, they’re extremely helpful.

Questions about spiral bits though… I’ve read that down-cut bits can actually push the router away from the workpiece, where up-cut bits pull the workpiece towards the router, which seems good. wondering if anyone else has heard or experienced this??

Other thing is that my next project will have some curves so if I use a spiral bit, will I not have to worry about grain direction??

-- Ben from IL

View Wdwerker's profile


333 posts in 3156 days

#13 posted 12-07-2012 02:36 PM

Make your templates index so they can be used on both sides of a part. Always route downhill on a curve to avoid the bit trying to lift the grain. Put the template on the other side and the cut will always be downhill.
Another cure is 2 different bits, bearing over the bit in addition to bearing on the bottom. Set up 2 routers and work from both sides of the board with the template staying in one position.

-- Fine Custom Woodwork since 1978

View gfadvm's profile


14940 posts in 3612 days

#14 posted 12-08-2012 03:07 AM

There is a third option. Grizzly has several flush trim bits where the cutter has some angle (I think they call them shear cut flush trim). They are inexpensive and work better than regular straight flush trim bits but not as well as the much more expensive spiral cut bits. I have several and they get a lot of use.

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

View live4ever's profile


983 posts in 3932 days

#15 posted 12-08-2012 03:24 AM

Go with the ultimate: William Ng’s big daddy pattern bit. No experience with it, but I kind of want one!

-- Optimists are usually disappointed. Pessimists are either right or pleasantly surprised. I tend to be a disappointed pessimist.

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