Search found 60 matches

by David Malicky
Mon Aug 13, 2012 7:58 pm
Forum: Flat-Top Acoustic Guitars and Bass Guitars
Topic: Purpose of bridge pins?
Replies: 141
Views: 52384

Re: Purpose of bridge pins?

FBD's are not used in themselves to analyse internal forces or flexible components, The body is isolated from contact to allow reaction forces to be determined. Agreed, of course, that FBDs cannot be used to find forces internal to the free body--that's implicit to the concept and discussed on page...
by David Malicky
Mon Aug 13, 2012 3:38 pm
Forum: Flat-Top Acoustic Guitars and Bass Guitars
Topic: Purpose of bridge pins?
Replies: 141
Views: 52384

Re: Purpose of bridge pins?

Jeff, those cases have been examined in this thread. The first FBD on page 2 is the rigid case with Nfront at the front corner, and Nrear = 0 as explained in the text. Tip occurs for h > b. All the other FBDs are various ways of modeling the parts as flexible. For a glued bridge as on page 2, the ba...
by David Malicky
Sun Aug 12, 2012 9:38 pm
Forum: Flat-Top Acoustic Guitars and Bass Guitars
Topic: Purpose of bridge pins?
Replies: 141
Views: 52384

Re: Purpose of bridge pins?

Its too long since I did much analysis, but I think there is some confusion between action and reaction happening with some of those diagrams. Jeff, Could you provide more detail? It's important to get the FBDs right so we can make sense of the mechanics. If there's an error, I would like to know a...
by David Malicky
Sat Aug 11, 2012 10:15 pm
Forum: Flat-Top Acoustic Guitars and Bass Guitars
Topic: Purpose of bridge pins?
Replies: 141
Views: 52384

Re: Purpose of bridge pins?

Thanks, Chuck. Good point on the magnitudes -- the break angle is on the shallow side, so A is relatively small as shown. The R peak is probably much taller right in front of the pin hole, and much shorter between the pin holes. And the "camel hump" peak under the saddle could be tall or short, depe...
by David Malicky
Sat Aug 11, 2012 6:08 pm
Forum: Flat-Top Acoustic Guitars and Bass Guitars
Topic: Purpose of bridge pins?
Replies: 141
Views: 52384

Re: Purpose of bridge pins?

Below are two more FBDs of a pinned bridge, not including the string itself in the free-body. These show the effect of the string's break angle over the saddle, as Alan mentioned. The 1st FBD shows the string tension itself in 4 places. The 2nd shows how the tensions resolve into forces A and B, at ...
by David Malicky
Sat Aug 04, 2012 3:12 pm
Forum: Flat-Top Acoustic Guitars and Bass Guitars
Topic: Tulip Poplar?
Replies: 21
Views: 8892

Re: Tulip Poplar?

Poplar with a light green hue will change to a honey color after about 5 days in the sun. White poplar goes to light honey, and any dark green/gray/purple areas go to dark honey. Very pretty! If you want to keep it light, choose a finish with UV inhibitors. Taylor made a batch of tulip poplar GA gui...
by David Malicky
Fri Aug 03, 2012 3:15 pm
Forum: Flat-Top Acoustic Guitars and Bass Guitars
Topic: Purpose of bridge pins?
Replies: 141
Views: 52384

Re: Purpose of bridge pins?

To clarify a few things, as Barry noted, there is always a torque (rotational force) on the bridge, unless a tailpiece is used. As Alan found, the only thing that affects the torque is the height of the strings off the soundboard. A free-body diagram of a pinless bridge (below) shows these effects c...
by David Malicky
Fri Aug 03, 2012 3:33 am
Forum: Flat-Top Acoustic Guitars and Bass Guitars
Topic: Purpose of bridge pins?
Replies: 141
Views: 52384

Re: Purpose of bridge pins?

Below are two "free-body diagrams" of 2 pinned bridges, to help understand the effect the various forces and assumptions. For both, the "free-body" is defined as including the bridge, saddle, most of the pins, and bit of string between the saddle and the bottom of the bridge (since all these are ins...
by David Malicky
Wed Jul 04, 2012 3:02 pm
Forum: Flat-Top Acoustic Guitars and Bass Guitars
Topic: William Cumpiano Interview
Replies: 24
Views: 53897

Re: William Cumpiano Interview

Charlie, I believe Cumpiano and Natelson could easily get their book into digital form? I just had this done on a book-length typewritten manuscript. It can be done relatively inexpensively and, once done, the book can be edited/rewritten/manipulated as easily as any computer-generated document. Go...
by David Malicky
Mon Apr 16, 2012 3:02 pm
Forum: Wood and Materials Q&A
Topic: Roasted Wood
Replies: 8
Views: 8541

Re: Roasted Wood

Tristan, very nice--I wish we had Thermo-wood in the US big box stores. There is some acetylated wood sold here (Accoya, from the UK), which studies show has lower damping and hygroscopicity (what a word... but that's what they call it). I need to drive to LA to see it, though.
by David Malicky
Tue Apr 10, 2012 2:41 pm
Forum: Tools and Jigs
Topic: Fox Bender - what am I doing wrong?
Replies: 13
Views: 13090

Re: Fox Bender - what am I doing wrong?

With the blanket between the wood and form, and aluminum on top, the outside of the mahogany is probably not so hot, as Mario mentioned. Can you check the temp on the outside of the wood? For the outside slat, stainless steel conducts less than steel, and of course, aluminum. For slats, the best I'v...
by David Malicky
Tue Apr 03, 2012 11:58 pm
Forum: Tools and Jigs
Topic: Replace a 3 phase motor with single phase; equivalent power?
Replies: 43
Views: 34987

Re: Replace a 3 phase motor with single phase; equivalent power?

Good one, Halgeir! Usually spindle reverse is done electrically, often by a forward-off-reverse lever on the carriage. Some higher-end lathes, mostly European I think, did instant spindle reverse via a clutch-pack and gears on an additional layshaft in the headstock. Curious what lathes have you see...
by David Malicky
Tue Apr 03, 2012 5:08 pm
Forum: Wood and Materials Q&A
Topic: Roasted Wood
Replies: 8
Views: 8541

Re: Roasted Wood

Oh, yes, that's something else entirely. The wood science folks call that "heat treated" -- sounds like kiln operators prefer "roasted"? Lots of scientific studies show it is much less hygroscopic, ~50% less. Usually, it's even more dimensionally stable for the little moisture it does take in. Great...
by David Malicky
Tue Apr 03, 2012 3:38 pm
Forum: Wood and Materials Q&A
Topic: Roasted Wood
Replies: 8
Views: 8541

Re: Roasted Wood

Sounds like "cooked" wood, which is common practice in lutherie. Taylor cooks ~all their wood -- 200F for tops, 270F for most everything else. 200F for 2 hours seems pretty common for tops. The idea is to 'set' the resins and remove all moisture, which preshrinks the wood so it is more stable. There...
by David Malicky
Mon Apr 02, 2012 1:34 am
Forum: Tools and Jigs
Topic: Replace a 3 phase motor with single phase; equivalent power?
Replies: 43
Views: 34987

Re: Replace a 3 phase motor with single phase; equivalent power?

Other uses for reverse: backing the tap out after power-tapping with the tailstock, getting a drill bit unstuck that's in deep and packed with chips, cutting angles with the compound (often better access), cutting internal grooves so you can see better, cutting external threads by leaving the half-n...
by David Malicky
Sat Mar 31, 2012 7:17 pm
Forum: Tools and Jigs
Topic: Replace a 3 phase motor with single phase; equivalent power?
Replies: 43
Views: 34987

Re: Replace a 3 phase motor with single phase; equivalent power?

Well, it's definitely not setup for 220, but I'm not sure if it's setup correctly for 110, either. I'm not an electrician, nor a motor expert, so hopefully someone else could give better info. In the pic, each of the Line inputs ("L") appears to be connected to 3 other wires: Line on the left is con...
by David Malicky
Fri Mar 30, 2012 1:59 am
Forum: Tools and Jigs
Topic: Replace a 3 phase motor with single phase; equivalent power?
Replies: 43
Views: 34987

Re: Replace a 3 phase motor with single phase; equivalent power?

Nice lathe, and lathe-doorway! Congrats on getting it ~rolled in. Yeah, I bet it was sweating. That's a fine fellow indeed... it's always fun to see someone else's setup. Is there a Z-axis motor for the CNC? Or did it simply rely on the geared auto-feed? I'm not sure if a 220V wired motor can be saf...
by David Malicky
Fri Mar 30, 2012 12:53 am
Forum: Tools and Jigs
Topic: Replace a 3 phase motor with single phase; equivalent power?
Replies: 43
Views: 34987

Re: Replace a 3 phase motor with single phase; equivalent power?

I've been around machine tools all of my working career and I've never heard of one type of motor making a better finish than another. Is that some kind of old wives tale? It's a good question. I've not seen any scientific studies on it, but there is a physical basis for it being real, and many rep...
by David Malicky
Thu Mar 29, 2012 3:03 pm
Forum: Tools and Jigs
Topic: Replace a 3 phase motor with single phase; equivalent power?
Replies: 43
Views: 34987

Re: Replace a 3 phase motor with single phase; equivalent power?

That sounds like a great trade. 1 HP should be plenty, even at higher speeds. Hope the drive wasn't *too* interesting. Great to have the chucks and faceplates -- as you know, tooling $ can kill the budget. I bet they are good quality, given the lathe maker. The camlock mount is remarkable, especiall...
by David Malicky
Wed Mar 28, 2012 11:47 pm
Forum: Glues and Finishes
Topic: Gummy Zinsser SealCoat
Replies: 12
Views: 6547

Re: Gummy Zinsser SealCoat

I use Sealcoat regularly as a base, to pop the grain (not under paint). Drying indoors, I scuff-sand 1 hour after application, with no problems. There is a dust load on the paper, but it's not gummy. Occasionally, I've RO sanded it 12 hours later... also just dust. I wonder if you have a bad batch, ...