Official Luthiers Forum!

I just completed the bridge making jigs that John How has listed in the "Jigs, Tool & Techniques" section. Nicely presented and fairly easy to make using the pictures and text John submitted...Thanks, John.

I plan to use a 1/8" saddle slot. I tried the only 1/8" bit (straight)I had on hand in some scrap. The quality of the slot was poor in oak.

My question...do I need an upcut or downcut spiral bit for this operation? TIA

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JJ
Napa, CA
http://www.DonohueGuitars.com

HI JJ

For the cleanest Cut you want a Down Cut Spiral, Upcut is for when you need quick chip clearance,

Guess what! for this job ideally you want both, such bits do exist that are both Up and Down cut and that would be the optimum.

Failing that I would go with a down cut spiral. This is what I use for saddle slots.

Until the other day and a conversation with Colin I didn't realise a Down cut was suitable for binding channels, and what a difference it makes to them.

I agree. Down cut is the way to go. Mostly because you want the cleanest, flattest bottom possible. A down cut bit delivers this.

Hi JJ

I just checked and the combined spirals only start at 12.7mm (1/2 inch). So thats not an option.

Downcut it is.

Thanks for the quick answers!

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JJ
Napa, CA
http://www.DonohueGuitars.com

JJ, it sound like you're assuming that the poor cut quality was due to the straight cutter geometry. I would look at other variables, since a straight cutter (or up, or down) is perfectly capable of making a mirror finish cut.

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John Watkins
CNC Guitar Parts

You might want to check the bearings in your router. No bit will give good results with a worn bearing. Yea, I learned this the hard way.   

     What you need is a good sharp bit. I know some of you will disagree but downward spiral bits in a closed hole or slot does not allow for proper chip clearance. As a toolmaker I can tell you this will get you in trouble very fast in a shop.Most people will have poor results by improper feed rate or dull bits .
      If the chips can't clear they will bog the cutter and dull the tool faster. ALso if your tool is low powered you will not have a good result. Speed and cutter sharpness are most important.
John hall

I just got my MLCS 1/8" spiral (upcut) in the mail, and used it in the drill press at 8500rpm (the fastest my drill press would go) to cut the slot in an ebony bridge...the cut quality is great, but the slot is a little oversized width wise...I guess my 40 year old Craftsman has some runout at those speeds! I wish MLCS offered a 3/32" cutter...that'd probably nail 1/8" for me...now I gotta use a thicker saddle blank after I just got 24 1/8 inchers in the mail!

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http://www.presnallguitars.com

You're probably right, John. In later trials today I had much better results practicing on scrap ebony and rosewood. I now feel that I can get acceptable results with the straight bit. Nonetheless, I'm still planning on purchasing the down spiral bit to compare.

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JJ
Napa, CA
http://www.DonohueGuitars.com

I'm going to have to agree with John on this one. The last 3 bridges I routed, I used a cheap 1/8" steel router bit I bought at Ace Hardware, primarily because thats what I had on hand. All 3 of them came out as my daddy used to say "slickern a gut" . I will admit I haven't used a dowcut spiral for saddle slots though.

Hi JJ,

I used both up and downcut spiral bits I bought from StewMac. I busted three of them and quit using them for saddle slots. After the first break, I called StewMac and they sent me another for free. After the 2nd and 3rd, I figure it's something I'm doing. I just never could get a good cut. Now I use a table saw with the same blade I have for cutting fret slots, and it works like a dream. Perfect slots with a very clean bottom.

Good luck!

John

How would you use a table saw for a saddle slot in a steel string bridge?

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JJ
Napa, CA
http://www.DonohueGuitars.com

Is it a thru slot like Mario's?

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http://www.presnallguitars.com

For an 1/8th slot ,i use a 3/32 " downcut . After reaching correct depth , I pack the fence with tape until I reach the correct width. Works well , and the saddle is snug.

I have made a base for the router which is perfectly square. To enter the bridge , I lean it over on it's right angle side, and slowly lower it to the saddle position (keeping the front of the base firmly against the fence). This way I can use multiple passes and gain a clean entry each time.

KiwiCraig

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CRAIG LAWRENCE of AUSTRALIA
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I use a downcut bit and take it slow with an air-line blowing into the slot as I go, which keeps the slot clear, though I never had any trouble without. I agree though that the most important thing is the bearings on the router/dremmel.

For binding channels though, downcuts are the bees knees. (I nearly used a simile referring to part of a dog's anatomy, but I think Lance might have censored that!)

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

I too use a 1/8" downcut in a lam trimmer for the saddle slot with good results.

I also agree with Colin (I think!) about the binding channels, I get better results with the downcut spirals than bearing / cutter sets for this.

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Rian Gitar og Mandolin

[QUOTE=BruceH] You might want to check the bearings in your router. No bit will give good results with a worn bearing. Yea, I learned this the hard way.    [/QUOTE]

I learned the hard way as well on a rosette. The bearings in the Dremel Pro is natorious for run out. The tool is not really designed for as tight tolerance milling as we use them for. I bought the new XRT and it is better but I like my Foredom rotary tool better for this job. I use it on a Stew-Mac base and a home made fixture using down cut spiral bits. As other have said, a std mill bit will not clear the chips and tend to push off causing an over size slot

I wouldn't even consider a Dremel for a saddle slot. I built the jig for a laminate trimmer just like Johnny Cool recommends. In fact, I use the same PC model as shown in his pictures.

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JJ
Napa, CA
http://www.DonohueGuitars.com

Hi JJ, I tried to respond this morning but my input got lost in cyberspace somewhere. I'm at work now so I'll try again.
I think my bit is 1/8 upcut spiral. I rout the full depth in one pass to get the tightest saddle fit I can. I have never had a problem with chipout and if I did it would be minimal and I reshape the bridge top anyway after routing the slot so that would clean it up anyway. Just make sure you mark the jig so the router always faces the same way because on that particular router, the bit is centered side to side but not front to back.
Glad you built one and I hope you enjoy it.

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Tickle your guitar daily, and it'll tickle you back.

John ...I oriented the router to pass just like you explained in the instructions.

Really...a single pass! That's impressive! I made at least 4 passes...it's tricky to have the bit enter on a straight vertical path each time it enters the slot, but after a little practice, I was able to do it consistently without any noticeable wandering. I'd love to know more about your single-pass technique.

- How deep do you make your slot?...mine is about .225"
- What's your theory on the upcut as opposed to the downcut as others in the thread have recommended?
- Does the upcut eject the chips upward and out of the slot and the down cut force the chips to the bottom?...or is it counter-intuitive?

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JJ
Napa, CA
http://www.DonohueGuitars.com

The downcut spiral bit cuts with a shearing action from top to bottom. The upcut spiral bit cuts with a shearing action from bottom to top. So the downcut starts it's cut at the surface of the timber, whereas the upcut ends it cut at the surface, with therefore a very small chance of tear-out at the surface. for most jobs they would be interchabgeable but for binding channels it makes sense not to have the cut finishing at the face of the soundboard.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

JJ, when I cut the slot, I have the router oriented the way I want and firmly against one edge or the other. The router is tilted so that the cutter is not touching the wood. I start the router and rotate the router into the wood till it is sitting flat, then I start moving across the bridge. The depth of my cut is about 2/3 of the bridge thickness probably about the same as yours.

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Tickle your guitar daily, and it'll tickle you back.

I use up spirals for all of my routing (which I do kind of a lot of) and I don't believe I've ever had a surface chipout.

Chip size and evacuation are the keys here. There's no point in getting a good chip load if you're going to cut every chip 100 times. That's why buried cuts are not recommended for a finish pass and doing them with a downcut spiral is really not good.

If you really want a good finish and a predicable slot, use a .0625" cutter. If you're using a full width cutter, I would use a 2 flute up spiral in Rosewood, 1 flute straight in Ebony.

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John Watkins
CNC Guitar Parts

Thanks to all the Johns as well as others who have chimed in. I've learned a lot this weekend building the jig and a lot more hearing from the more experienced on this post.

I love this place!

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JJ
Napa, CA
http://www.DonohueGuitars.com