| Official Luthiers Forum! http://luthiersforum.com/forum/ |
|
| Calculating dovetail offsets http://luthiersforum.com/forum/viewtopic.php?f=10101&t=31696 |
Page 1 of 1 |
| Author: | ernie [ Thu Mar 31, 2011 6:12 pm ] |
| Post subject: | Calculating dovetail offsets |
I have an older set of LMI 1/4in aluminum dovetail jigs meant for a classical guitar, that I would like to use . I have them seperately mounted on a frame, The alum mortise jig will accept up to a 5/8in guide bushing, my problem consisits of matching the correct bushing size to a matching router bit calculating the offsets makes my head spin . I have 4 large routers and 3 med routers and a host of laminate trimmers . I would prefer to use either the med size or large routers for this job. Has anyone out there calculated the right combo of straight bit/dovetail bit / guide bushing. I have two 5/8in guide bushings on the large routers. The med size bosch router needs a sliding adapter to mount the bushings currently 6 weeks backordered . Any suggestions would be much appreciated. Thanks ernie |
|
| Author: | nickton [ Fri Apr 01, 2011 2:10 am ] |
| Post subject: | Re: Calculating dovetail offsets |
I would think as long as you use the same bushing for both cuts it should work with whatever dovetail bit you use, but maybe I'm misunderstanding here. I know I can "over think" at times and must remember the principle of KISS.  here's my dovetail jig. Works for me. Not even sure what size bushing I use in my Porter cable router. Hope that helps. |
|
| Author: | ernie [ Fri Apr 01, 2011 6:57 am ] |
| Post subject: | Re: Calculating dovetail offsets |
I want to use 2 seperate bits the first 3/8in wide by 1/.2 in shank to hog out 1/2 in of waste and then use a 1/2in shank/1/2 in dov bit to make a slightly lower cut by 1/16in of my target depth 1/2in and then cut a final pass with the dov bit at 1/2in. depth The slightly lower 1/16in is for future neck removal ?? Is this how you do it ?/ or do you just use one size bit to do the mortise and tenon ?? PS all done with a 5/8in OD collar |
|
| Author: | TonyKarol [ Fri Apr 01, 2011 7:12 am ] |
| Post subject: | Re: Calculating dovetail offsets |
What bit/guide does the jig recommend to use ??? .. I doubt you can just change to whatever you want because the bottom of the female template will dictate how large a dovetail will drop to the bottom after routing the male side. If the bottom of the female template will take a 5/8,and its afarily tight fit, then the bottom of the route will be the size of the dovetail bit, not much larger, correct - so in your case, 1/2 inch. But when you use a larger guide on the male template, you get a much wider, rounded dovetail end .. the angles will be correct , but no way will the male bottom out into the female pocket ... do you understand ??? Take a look at the dovetail jig shown above .. there is no way a larger guide will give you the pointed narrow tip in the male to fit into a tight bottomed pocket - the neck will sit way too high, above the top of the block. |
|
| Author: | ernie [ Fri Apr 01, 2011 8:16 am ] |
| Post subject: | Re: Calculating dovetail offsets |
Your right Tony I am flying blind and trying to guess the sizes , and that is what happened. the male dovetail was too high, but I was using 1/4in bits on that try. The female dovetail will accept up to a 5/8in collar. I called LMI where I purchased the templates , and they had no clue of which router bits to use with their 1/4in alum. dovetail templates and I don/t have a copy of the original data sheet (lost). My dilemna is figuring out which combination of straight and dovetail bits will work to create the joint . I would like to use the straight bit to hog out most of the waist, and then use the dovetail bit to make one pass at 1/16in below my targeted depth of 1/2in and then a final pass at 1/2in. Your thoughts please . thanks ernie |
|
| Author: | Corky Long [ Fri Apr 01, 2011 8:42 am ] |
| Post subject: | Re: Calculating dovetail offsets |
I think this is a case where I'd experiment on scrap. Dovetail geometry gives me a headache - perhaps that's why I shifted to M&T bolt ons. Will a couple of test cuts on scrap blocks work for you? |
|
| Author: | Robbie O'Brien [ Fri Apr 01, 2011 9:07 am ] |
| Post subject: | Re: Calculating dovetail offsets |
Ernie, Watch those videos I sent you and you will find what you are looking for. Anyone else interested in making this jig, LMI has plans and a hardware kit that includes the templates. Setting up the jig The dovetail joint The M&T joint |
|
| Author: | ernie [ Fri Apr 01, 2011 10:31 am ] |
| Post subject: | Re: Calculating dovetail offsets |
Thanks robbie I already bought the plans from you. ernie This old LMI template is 1/4 in alum 
|
|
| Author: | ernie [ Fri Apr 01, 2011 2:16 pm ] |
| Post subject: | Re: Calculating dovetail offsets |
Hi robbie watched the video . I learned a lot thank you . First problem is that the LMI jig is not adjustable therefore one needs to make the tenon jig as close as possible to the target length. Secondly. I have an older makita router with a 5/8in collar the I.D. of the collar is 14mm O.D.is 16mm I believe you used a 1/2in width and depth dov bit on 1/2 in shank ?? coupled with a 3/8 in st bit with 1/2 in shank. I have perhaps the same bits, but because your I.D. is 17/32 your offsets are much smaller than the setup I just used on a dummy piece. I need to find a bushing that is 17/32 in order to make a complete dovetail mortise ?. When I looked into the mortise cavity about 4mm at the top had not been cut. MY dovetail bit is 7 deg 1/2in wide and 1/2 in length with 1/2 in shank . The st . bit is 3/8in wide by 1in long on 1/2 in shank. Do you think changing the guide bushing to 17/32 will help ?? . I only one one mid size PC router circa 1976. It has a 1/4 in collet on it , and it/s a pita to change settings. The male tenon was way too big , probably too much offset ?? Your suggestions Robbie would be appreciated thanks again ernie. I am determined to solve this ____ problem. |
|
| Author: | ernie [ Fri Apr 01, 2011 2:27 pm ] |
| Post subject: | Re: Calculating dovetail offsets |
OOps just checked again. The dovetail is 14 deg . not 7 as per your video . Thats probably why there is a 4 mm st ledge on upper mortise cavity. |
|
| Page 1 of 1 | All times are UTC - 5 hours |
| Powered by phpBB® Forum Software © phpBB Group http://www.phpbb.com/ |
|