# spiral bits



## stacewb (Mar 7, 2012)

what is the diffrence between up and down cutting


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## The Warthog (Nov 29, 2010)

staceywb said:


> what is the diffrence between up and down cutting


With an up-cut bit, the chips are drawn up out of the slot you are cutting. This may leave a slightly rough edge at the top of the work. A down-cut bit leaves a clean top, but a slightly ragged edge at the bottom if you are making a through cut. The down cut bit also goes slower as the chips have a harder time getting out of the way if it's not a through cut. I have an up-cut bit that I use for cutting circles. I plan to start cutting mortises this year, with the up-cut bit.


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## Mike (Nov 22, 2004)

Bill, this common question is just one of the useful things covered in the Sticky threads. Save yourself a lot of time by reading them.


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## KenBee (Jan 1, 2011)

The Warthog said:


> With an up-cut bit, the chips are drawn up out of the slot you are cutting. This may leave a slightly rough edge at the top of the work. A down-cut bit leaves a clean top, but a slightly ragged edge at the bottom if you are making a through cut. The down cut bit also goes slower as the chips have a harder time getting out of the way if it's not a through cut. I have an up-cut bit that I use for cutting circles. I plan to start cutting mortises this year, with the up-cut bit.


I am using an upcut bit for cutting circles also, but I just bought a 1/4 inch compression bit I want to try once the weather permits me access to my workshop. My part of "Sunny California" is neither sunny or warm these days. :angry:


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## Quillman (Aug 16, 2010)

"what is the diffrence between up and down cutting?"

See no. 12.


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## KenBee (Jan 1, 2011)

Quillman said:


> "what is the diffrence between up and down cutting?"
> 
> See no. 12.


Hi Pat....On a router table you can upcut only and with a hand held router you can only down cut, that is if you don't lay on your back to use the hand held router. 

Actually I am just trying to figure out where a Spiral Compression Bit fits into the scheme of things. In my opinion it will do no more than using an upcut or down cut spiral bit separately for the job at hand. Another thing to take into consideration is the cost of a Compression bit. In most cases a downcut and upcut bit can both be bought for the cost of one compression bit. From my experience the tear-out generated with a spiral bit is not enough to be concerned about because I always touch sand my edges anyhow. I used an upcut bit with my circle jig on a piece of 1/4" Birch plywood a couple of days ago and the tear-out was for all intents and purposes nil.


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## Quillman (Aug 16, 2010)

"where a Spiral Compression Bit fits into the scheme of things"
*****************

It (compression spirals) has its place.
But on close inspection you'll see the transition zone on the work is boogered.
So, for example, if you were to join edges produced from a compression cutter, they will rock and roll.
These are CNC tools, best with 5/8 and 3/4" shanks, finish cuts too, not for joinery.

In my view, Up or Down spirals have no sensitivity to stationary or portable machinery.
The issue is fixturing. If you can hold on to the work it matters not which of the 3 spiral tools you use on the router table. With the hand held router there are surprises either way.
I tell my students to get some priors with straight flutes first, then we talk about the solid carbide spirals and their limited selection compared to ordinary straight bits.


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## Phil P (Jul 25, 2010)

Ken Bee said:


> Actually I am just trying to figure out where a Spiral Compression Bit fits into the scheme of things. In my opinion it will do no more than using an upcut or down cut spiral bit separately for the job at hand. Another thing to take into consideration is the cost of a Compression bit.


Hi Ken

As Pat says spiral compressions are really a CNC solution to a particular problem - the problem of routing double-faced laminated or melamine faced boards (particle board or MDF) in one hit. For that they are excellent, but as he says the point where the up and down spirals meet is boogered - in fact you often get a large dark witness line from 1 to 3mm wide where the fibres are really trashed. This isn't a problem if you are going to apply an ABS or PVC edging or a solid wood lipping after machining. which is what happens with most CNCd stuff processed with compressions, but it is far from ideal on shown edges in solid wood work

Regards

Phil


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## KenBee (Jan 1, 2011)

Quillman said:


> "where a Spiral Compression Bit fits into the scheme of things"
> *****************
> 
> It (compression spirals) has its place.
> ...


Hi Pat...I did a little more research on the Compression bit and learned it is basically a CNC bit most often used to cut/trim plastics, melamine, etc.

I at least did't pay all that much for it so if I never use it it will not be a great loss.

I have been cutting out circles with the Jasper Circle Jig using a 1/4" Spiral Upcut Bit fitted in my PC 892 plunge router with great results in both 1/4 and 1/2 inch Baltic Birch ply. The 1/4 inch I do in one cut, whereas the 1/2 inch I do two 1/4 inch cuts. I am partial to the spiral bit because of its ease of plunging and smooth, effortless cutting action. My next test so to speak is using it to cut out recesses for clock movements in hardwoods such as Red and White Oak, Maple and Walnut. I don't have a true straight flute plunge bit and yes I know a regular straight flute bit will plunge, but for some reason or other it disturbs me when the straight flute bit initially bites into the wood.


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## jschaben (Jun 21, 2009)

Ken Bee said:


> Hi Pat...I did a little more research on the Compression bit and learned it is basically a CNC bit most often used to cut/trim plastics, melamine, etc.
> 
> I at least did't pay all that much for it so if I never use it it will not be a great loss.
> 
> I have been cutting out circles with the Jasper Circle Jig using a 1/4" Spiral Upcut Bit fitted in my PC 892 plunge router with great results in both 1/4 and 1/2 inch Baltic Birch ply. The 1/4 inch I do in one cut, whereas the 1/2 inch I do two 1/4 inch cuts. I am partial to the spiral bit because of its ease of plunging and smooth, effortless cutting action. My next test so to speak is using it to cut out recesses for clock movements in hardwoods such as Red and White Oak, Maple and Walnut. I don't have a true straight flute plunge bit and yes I know a regular straight flute bit will plunge, but for some reason or other it disturbs me when the straight flute bit initially bites into the wood.


Hi Ken - If I remember correctly, you picked up one of those Onsrud 3/8" compression spirals off eBay. For what you are doing, just routing clock reliefs, I think that bit would work wonderfully.The "transition area" shouldn't be a big deal for you as that edge isn't exposed and on that bit, it doesn't occur until you are a half inch or so into the cut. I picked up the same bit and used it to radius some corners and cut some holes in 3/4" A/C plywood and the thing is great, very, very sharp and nice clean cuts.


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## KenBee (Jan 1, 2011)

jschaben said:


> Hi Ken - If I remember correctly, you picked up one of those Onsrud 3/8" compression spirals off eBay. For what you are doing, just routing clock reliefs, I think that bit would work wonderfully.The "transition area" shouldn't be a big deal for you as that edge isn't exposed and on that bit, it doesn't occur until you are a half inch or so into the cut. I picked up the same bit and used it to radius some corners and cut some holes in 3/4" A/C plywood and the thing is great, very, very sharp and nice clean cuts.


Hi John...Yes I did buy two Onsrud bits off Ebay, but they were the 1/2" up and down cut "Chipbreakers". I agree they are sharp because just looking at them makes my fingers bleed.  Being 1/2" bits they will not work with the Jasper Circle Jig which is laid out for use with a 1/4" bit even though I may break out some scrap wood and try to use the 1/2" bits by compensating for their size to cut out the hole size I need. I need to cut some round pieces to use as wedges when using my Woodhaven Planing Jig so that may be a good test for something that doesn't have to be exact. 

I did buy a 1/4" Compression Bit off Ebay for $14.50 and after looking at it yesterday I discovered it is a Whiteside bit so $14.50 for it could be considered grand theft considering they sell for over $35.00 about anywhere you look.


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