Accurate templates: advice needed

[Jason Rodgers]

Howdy, folks. In an attempt to improve accuracy and repeatability in my work, I've made some templates of a bridge base plate. They should serve as a drilling guides, as well as outline and centerline references. I think the pictures will explain a bit...

The templates are in 1/4" fiberboard (reinforced with CA after this picture).

This bridge base prototype was made with 1/4" phenolic sheet. The template was double-stick taped (woven carpet tape) to the phenolic, outline scratched, and holes drilled. I cut the rough outline on the bandsaw, and then refined on the disc sander.

These bridge plates will utilize Graph Tech Wilkinson saddles (I've seen a number of folks using this solution for multi-scale bridges).

Looks pretty cool, but there are some issues. First, I need to re-think the string-through-body escape hole: the largest hole on the plate is long enough for a range of intonation adjustment, but being a circular hole, is too wide for the saddles' height-adjustment screws to stradle. It really should be a slot. I'll fix that on version 2.0.

The biggest problem, though, is that I really need to drill those saddle post screw holes VERY accurately. Here's where I need the advice. How does one mark out and drill holes and get them to go where you want, using basic layout skills and a drill press? My work is very close, but the saddles are clearly not equally spaced on the plate. Should I ditch the fiberboard and use the phenolic as the template? Once I do that, how do use the template as an accurate drilling guide?

Eventually, after I work out the design bugs on these templates and prototypes, I'd like to get the plates sketched up in CAD and have someone crank out a batch on a CNC. In the meantime, I need to be able to produce these with reasonable accuracy by hand.

Thanks for the tips!

[Michael Lewis]

If your fiberboard templates are as accurate as you want you can reinforce the holes with metal drill guides. They are bushings made just for such application, and there are several styles and sizes.

As for marking where to drill I suggest you get a set of transfer punches at Harbor Fright. I think a set costs about $10, and they come in handy for many situations. Transfer punches are sized metal shafts (similar to a set of drills) with a center punch tip, so you select the diameter to fit your template holes and the punch can't help but make a center punch mark right in the center of the hole. Your drill should not wander from that unless it is poorly sharpened.

[Mark Swanson]

Looks good Jason! Hey, where did you get those bridge saddles?

[Dave Weir]

I make marking punches by taking the correct size drill bit and putting it upside down in a cordless drill and then with the drill running sand a point onto the back end with a belt or spindle sander. Then drill half way into a little piece of dowel and glue it in. I only use a few specific sizes.
For tuner holes, I used the head stock of a neck that didn't work out and drilled the holes and glued 1/4" mild steel to it and drill through the steel. The steel goes against the real head stock so by the time the drill bit gets to it, the scrap wood has it pretty well lined up. I think it will last for quite a few guitars, but if it seems to wear I'll replace the mild steel with something heat treated.

[Jason Rodgers]

When it came to marking out my fiberboard templates, I used a fine-tip Sharpie, punched by an awl point, drilled with bradpoint bits. Thinking this through out loud, my first step may be one of my problems: that pen point is 1/32" wide, which could be exactly on top of the true line, a little to either side, or that whole 1/32" off. Do that with the neighboring lines, and now that error is compounded, and that's why I see two saddles touching at the E and B, and a full 1/16" away at G and B.

On my next attempt, I'll use the phenolic for the templates, do all my layout with a marking knife, and look into drill guides, as Michael suggests. If I can do this accurately, then, when it comes to transferring these holes, I probably first need a more solid means of attaching the template to the work. Maybe a spot of CA shot with accelerator? And finally, the transfer punches.

Mark, I've been getting a bunch of guitar parts through amazon. The Graph Tech Wilkinson bridges are about $35 per set. I used them on my 7-string. The cool thing with not having the anchor/intonation screw coming from behind, like on a Fender bridge, is that you can pivot the saddles a bit to adjust string spacing. The un-cool thing about that, though, is it looks messy and half-assed.

Thanks, guys!

[Alan Carruth]

You'll probably need to go to something harder than fiberboard to get better accuracy. I often use Plexi for templates for wooden parts, and aluminum when I want to be more accurate.

On plexi you can simply scribe lines to locate things. On aluminum you can use a Sharpie to blacken the surface and scratch lines into that. They show up really well.

To get a hole accurately placed it's best to sneak up on it. Decide on reference points or edges on the part and measure everything from there. Scribe lines to locate the holes and center punch them. Use a small bit to drill out a pilot hole, and measure the location accurately from your references. If the hole is not where it should be notch one edge in the direction you want the hole to move, and re-drill with the next size larger bit. The notch will cause the bit to start cutting on that side and move the hole, maybe as much as .005". Keep checking and notching until you get the hole where you want it.

As Micheal Lewis says, those steel guides are really handy for keeping the holes from wearing out. When I ran drill presses in a production shop, lo these many years ago, all the jigs were made of aluminum with hardened steel bushings, and they would hold tighter tolerances than you need for thousands of parts. If that seems like overkill, I'd bet a plexi jig with brass tubing inserts would hole up pretty well. There's a local hardware store that also sells thick walled stainless tubing that could be held in a plexi jig with CA. Countersink the end to help guide the drill in.

[Michael Lewis]

You can make your own guides as Alan describes, or go get commercially made ones from a Fastenall store, or order some from an industrial supplier like MSC or McMaster-Carr. It will help to look at an online catalog to see the different types available.

[Jason Rodgers]

Just to understand the type of wear we're talking about here, how many times could you run an 1/8" bit at 500rpm through a template hole before it starts getting loose or oblong?

I don't build a whole lot of instruments, and making templates doesn't mean I'm planning on going into big-time production, but I do want to make some "standard" parts to speed up construction and improve accuracy and consistency. I'm in the process of making templates for neck/fingerboard taper, pickup routes, control cavity and cover, headstock profile, etc. This bridge plate, as simple as it is, can suck up a lot of time with layout and shaping.

My ACE has some options for bushings and tubing and such. I'll investigate.

[Bob Gramann]

With some of my templates, I can tell you from experience that one or two times with the drill bit can widen the template hole. I remade the templates and use a punch to mark the hole. I no longer drill through templates. I didn't know about transfer punches as mentioned by Michael above. I'm going to get some.

Just as an aside, I pay extra to get polycarbonate (like Lexan) to make templates. It's a lot easier to work than acrylic (Plexiglas) and doesn't crack.

[Bob Gramann]

Update: I thought the transfer punches were such a good idea that I went to the local Harbor Freight and got a set. They go back tomorrow. Many of them were .005" or more off center. I will spring for a better set somewhere else.

[Jason Rodgers]

With some of my templates, I can tell you from experience that one or two times with the drill bit can widen the template hole.

Wow, okay then.

There are a variety of transfer punch sets on amazon, many for under $30 with free shipping. From reading some of the reviews, the higher the prices, the greater likelihood of the punches being accurate and hard enough to take a few taps.

Has anyone used a universal punch? It has a self-centering cone that fits in the hole, and a single tip to punch the center. I'm guessing you'd need to chuck this up in a drill press to get the shaft perpendicular on the x and y for an accurate center.

When it comes to an accurate transfer of points, I think that using a couple pins to lock the template into the work would be a good idea. For example, I could drill any hole, put a pin in it, drill any other hole on the other side of the template, put a pin in it, and now the template won't shift around, whether I use the template as a drill guide, or I'm banging on it with transfer punches.

[Bob Gramann]

Most of the cheaper sets seem to be the same Chinese made set that Harbor Freight sells. I've ordered a set with guaranteed .0005" tolerances. I'll see when they're delivered.

[Jason Rodgers]

Right, it even looks like Grizzly sells the same or similar set! Thanks for checking this out, Bob.

[Michael Lewis]

You can regrind the points. Not a lot more demanding than sharpening a twist drill. My set is the cheap stuff and rather soft metal, but I'm not working on steel. They do fine for brass and aluminum.

[Eric Baack]

The center punches are helpful

Also, a good set of Jobber size drill bits (short bits) makes a big difference to keep the bit from walking a bit.

[Jason Rodgers]

Stopped by ACE yesterday and picked up some 1/8" ID stainless tube and 1/8" OD brass rod. I'll give that a go.

Here's something else, though: I downloaded the free version of SketchUp, and have been playing around with drawing my bridges very accurately so that they could eventually be translated into tool paths (by someone who knows more about CAD/CAM that me!).

That looks pretty good! And hey, wouldn't it be great if I could just print this out, stick it to my work, punch the drill points, and Bob's yer uncle?

Here's my next challenge, then... how do I print it out full scale? There are all sorts of file types that SketchUp will export: pdf, eps, bmp, jpg, tif, png, exp, dwg, dxf. I tried it as a PDF, but that didn't work. I am not learned in these sorts of things.

EDIT: (sigh) Google is my friend, as is the help page on SketchUp. I am holding a full-scale printout of my bridge. Cool!

[Dave Weir]

It depends on the printer and version of windows, but there should be a "no scaling" option or "adjust to 100% of normal size."
You can get full size sheets of white lable paper with a peal off backing. I've used it for fan fret finger boards and it works great. Tape one half down with masking tape, then peal the backing off the other half and stick it down. Then lift the first half up and take off the backing.

[Jason Rodgers]

You can get full size sheets of white lable paper with a peal off backing.

This is a great idea to avoid distorting the paper template with glue!

[Jason Rodgers]

I just finished up a successful attempt at bridge plate version 2.0.

A 1:1 scale printed template drawn in SketchUp was glued with a thin smear of fish glue to a piece of 1/4" phenolic, and then I used an awl to punch the drill points. The print options in SketchUp give a high definition print that is very crisp and fine-lined. I buried my brad point bits in the chuck to minimize deflection, cranked the drill press up to 2300 rpm, and went for it.

I used needle files to blend the three holes that make the string-through slot. This was a little tedious, but doable in phenolic or wood. This would be challenging in aluminum or brass.

Testing the alignment of the saddles. It was VERY good.

Phenolic, being a plastic product, can be polished to a fine finish, but I just went up through 1500. The dull finish actually matches the Graph Tech saddles pretty closely.

Pretty damn sexy, eh?

Thanks for all the input here. I also want to thank John Sonksen, my local Garage Lutherie bro, for some big tips through email and phone conversations. When I think about the short turnaround between my first template attempts, to now, I'm really appreciative of the resources I have available to me. Until I can figure out a way to get these parts built on some sort of scale, I'm considering this process sustainable for my current (minuscule) output.

[David King]

One more trick Charles Fox tossed my way was to use ball bearing races instead of drill guides. Any hobby shop will have loads of 1/8 in. i.d. ball bearing for R/C model cars. Since the race spins with the drill there is no wear.

Of course the better way is to use an indexing pin on the drill press table and locate the holes on the backside of a fixture that holds your part. You can see what the heck is going on and the chips won't get all jammed up around the the drill flutes.

I do all my layouts on the milling machine to avoid having to resolve where the guide holes need to go. If you are patient you can use layout fluid and a sharp scratch awl and then use a magnifying center punch like this: http://www.use-enco.com/CGI/INSRIT?PMAKA=240-0404