Official Luthiers Forum!

Solely owned and operated by Lance Kragenbrink
It is currently Tue Sep 25, 2018 9:44 pm


All times are UTC - 5 hours


Forum rules


Be nice, no cussin and enjoy!




Post new topic Reply to topic  [ 27 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Getting circles straight
PostPosted: Thu Feb 15, 2018 6:38 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Fri Dec 17, 2010 6:22 pm
Posts: 1289
First name: Miguel
Last Name: Bernardo
Country: portugal
Focus: Build
Status: Semi-pro
see what i´ve done with the title? :)

anyway, a little help please. i made my first rosette groves with an home made circle cutter. they were circular and reliable.

then i upgraded to a stewmac thing with a dremel. i never got the circles to be perfectly circular - which puzzled me. i mean, the theory is pretty simple and fool proof and the result seemed concentric, the grove looked circular and ends met where they should but if i went at it with my manual cutter, refining the edges, there were always places where it cut more than others, normally from 5 to 7 o´clock it was a bit short. it was cumbersome to rout wood circles for inlay, as they never fit 100% - which meant quite some time fiddling with my manual cutter. the same happened with inlaying veneers strips. in some places they´d be a perfect fit, in others it´d be too tight or too loose. i blamed it on some poor manufacturing of my dremel tool.
so, eventually, i got a router and a circle cutting jig (home made one, like the Fleishman (?) one, but should work good) - and the same happens. i can get them 99% circular but not quite 100%. i can work around it but it bothers me, specially because there must be something simple im missing. i don´t suspect that a piece of TCT blade rotating at 30000 rpm would care if its cutting end grain or side grain of 1,2 mm thick soft spruce but who knows?

any ideas?

TIA,
Miguel.

_________________
member of the guild of professional dilettantes


Top
 Profile  
 
PostPosted: Thu Feb 15, 2018 7:12 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Mon Jan 28, 2008 5:21 am
Posts: 3829
Location: Central PA
First name: john
Last Name: hall
City: Hegins
State: pa
Zip/Postal Code: 17938
Country: usa
Focus: Build
Status: Professional
what bit you using? I have these and modified them for a die grinder . There are 2 problems with this design.
A only two points of attachment for the dremel this allows for a lot of slop and movement.
B you have to to take 2 passes one in and another out to allow for the slot in the center bushing

on top of this you need a good sharp bit. I do not use down cut bits in this as the chips end up in the bottom and this builds up heat

I use a fresh bit and none larger than 3/32

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Member Board of Directors ASIA
You Don't know what you don't know until you know it


Top
 Profile  
 
PostPosted: Thu Feb 15, 2018 7:34 pm 
Offline
Contributing Member
Contributing Member

Joined: Sat Aug 27, 2011 1:59 pm
Posts: 243
First name: Ken
Last Name: Lewis
City: Mt. Pearl
State: NL
Country: Canada
Focus: Build
Status: Amateur
What John said and make sure there's no play anywhere, especially in the center pin. You may be doing
this already but clamping the top to the work surface is a good practice also.



These users thanked the author Ken Lewis for the post: TimAllen (Fri Feb 16, 2018 1:26 pm)
Top
 Profile  
 
PostPosted: Thu Feb 15, 2018 8:41 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Tue Mar 01, 2011 1:32 pm
Posts: 3468
First name: Alex
Last Name: Kleon
City: Whitby
State: Ontario
Zip/Postal Code: L1N8X2
Country: Canada
Focus: Build
Status: Amateur
Maybe some runout in the Dremel shaft plus the transition from side to end grain can be part of the problem.

Alex

_________________
"Indecision is the key to flexibility" .... Bumper sticker


Top
 Profile  
 
PostPosted: Thu Feb 15, 2018 10:30 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Fri Dec 14, 2007 3:21 pm
Posts: 2623
Location: Alexandria MN
As mentioned earlier the two big issues for me have been less than a tight fit for the centering pin and forgetting to clamp the top to the work surface.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.


Top
 Profile  
 
PostPosted: Fri Feb 16, 2018 1:06 am 
Offline
Mahogany
Mahogany

Joined: Mon Oct 31, 2011 8:50 pm
Posts: 66
First name: Bob
Last Name: Howell
City: Atlanta
State: Ga
Focus: Build
Status: Amateur
I had this problem with Proxxon tool and cut down on error by drilling new pivot hole, carefully set at perpendicular. I still had slop so must keep tension even as I went around circle. Multiple rotations cancels out error. Don't notice it now.


Top
 Profile  
 
PostPosted: Fri Feb 16, 2018 8:05 am 
Offline
Brazilian Rosewood
Brazilian Rosewood
User avatar

Joined: Thu Jan 06, 2011 6:08 pm
Posts: 2678
First name: ernest
Last Name: kleinman
City: lee's summit
State: mo
Zip/Postal Code: 64081
Country: usa
Focus: Build
Status: Professional
FWIW if your using the stewmac jig with a die grinder or whatever tool you have to make sure that you align your bit with the center of the circle in the base of the stewmac circle cutter jig . My machinest friend centered it for me before adding the die grinder purchased from john hall. He is a very accurate machinest and said that the base needed squaring up which he did on his60+ k cnc milling machine including finding dead center on the stew mac base and making sure that the base itself was square which it was not. I am switching over to lathe tool bits for cutting grooves on the drill press . See peter howlet/ts video on turning a drill press fly cutter into a rosette cutter for uke or guitar rosettes on youtube


Top
 Profile  
 
PostPosted: Fri Feb 16, 2018 11:42 am 
Offline
Cocobolo
Cocobolo

Joined: Tue Jun 30, 2009 3:20 pm
Posts: 452
Focus: Build
i use a cnc mill and a down cut bit. results are more round then a wooden construct needs to be and the depth control is far better.

you can always use your homemade circle cutter to part the grain to size then use your fixture and dremel to cut out the waste. i did this for a while and it worked out fine.


Top
 Profile  
 
PostPosted: Fri Feb 16, 2018 1:17 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Fri May 14, 2010 11:43 am
Posts: 661
First name: Aaron
Last Name: Craig
City: Kansas City
State: Missouri
Focus: Build
Status: Semi-pro
As others have mentioned, a very tight and perpendicular hole for the index pin is a must. Sharp bits are essential too. And don’t try and cut the full depth in one pass. I am more aggressive with removal of the central portions of the channel, but I still take it down in multiple passes to the final depth. Once I’m down to the final depth, then I sneak up to the final inner and outer dimensions of the channel (i.e., for all prior passes, I am leaving a few thousandths on both inner and outer dimensions). Doing this negates the significant risk that your bit wanders off line while trying to hog out too much wood. If you are trying to take single passes at final dimensions, my guess is that’s where your issues rest. A small diameter end mill spinning at 30,000 rpm is actually surprisingly prone to wandering off track regardless of the jig used if you are attempting full depth cuts (not by much, mind you, but enough to cause gaps and tick you off - Ask me how I know).



Sent from my iPhone using Tapatalk Pro

_________________
Aaron Craig



These users thanked the author jac68984 for the post: TimAllen (Fri Feb 16, 2018 1:27 pm)
Top
 Profile  
 
PostPosted: Fri Feb 16, 2018 2:56 pm 
Offline
Walnut
Walnut

Joined: Sat Jan 04, 2014 12:22 pm
Posts: 14
First name: Roy
Last Name: Machin
City: Mexborough
State: South Yorkshire
Zip/Postal Code: S64 0HW
Country: United Kingdom
Focus: Build
Status: Amateur
I had the same problem and overcame it by gluing a bearing into a recessed hole in my workboard, same bore as the jig registration pin and used a brass rod in it and a square when setting verticality.

Roy


Top
 Profile  
 
PostPosted: Fri Feb 16, 2018 3:52 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Wed Apr 08, 2009 9:34 am
Posts: 2946
What they said. Use as thick of as a bit as you can get away with, and getting as much of that shank inside the collet as possible, even if you have to cut some off. You don't want much of the shaft showing outside the collet.
Consider that in different areas of grain, tops cut a bit differently. Cutting with the grain is easier, and may end up a little looser than end grain cutting.
I used to go full depth most of the time, but was using hard red spruce and a couple of good coats of lacquer rubbed in too. Consider the softness or hardness of the spruce you are using. Consider the speed at which you are routing the slots too. Final cuts mean VERY slow cutting both ways.

_________________
J. Brentrup Guitars & Mandolins
http://www.brentrup.com


Top
 Profile  
 
PostPosted: Fri Feb 16, 2018 9:02 pm 
Offline
Koa
Koa
User avatar

Joined: Mon Sep 05, 2011 10:45 pm
Posts: 1353
First name: Trevor
Last Name: Gore
City: Sydney
Country: Australia
Focus: Build
Status: Professional
Tight tolerances on the exactly perpendicular holes in the work board and top panel, large diameter pivot pin (10mm in my case), clamp the work to the board securely, rigid circle jig (but still don't lean on it) with zero backlash adjustment, precision aftermarket collets with minimal TIR and precise bits.

Attachment:
DSCF0391s.jpg


Gives the accuracy I want.

Attachment:
DSCF7793s.jpg


You do not have the required permissions to view the files attached to this post.

_________________
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au



These users thanked the author Trevor Gore for the post: Durero (Sat Feb 17, 2018 12:06 am)
Top
 Profile  
 
PostPosted: Sat Feb 17, 2018 4:36 am 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Fri Jul 10, 2009 4:44 am
Posts: 3419
First name: colin
Last Name: north
Country: Scotland.
Focus: Build
Status: Semi-pro
I taper the hole for the centre pin with a bridge pin reamer and tap in the pin with a small hammer while it is held vertical in the jig - no wobble or slack.
I also use a scrap of Teflon tape to take up any possible slack in the jig's centre pin hole but not create any friction.
I use a Makita laminate trimmer in a wells-carol type jig (no wobble like my old Dremel/SM jig) and fix the top my work-board with masking tape.

_________________
“There are two men inside the artist, the poet and the craftsman. One is born a poet. One becomes a craftsman.” - Emile Zola


Top
 Profile  
 
PostPosted: Wed Feb 28, 2018 6:07 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Fri Dec 17, 2010 6:22 pm
Posts: 1289
First name: Miguel
Last Name: Bernardo
Country: portugal
Focus: Build
Status: Semi-pro
thanks for the replies (and sorry if i´m late). there´s good advice here, some of which i already use (clamping work board, perpendicular pivot, multiple shallow passes, etc.) but some others worth investigating. as i said, it´s nothing i can´t work around but its annoying and a time waster.

cheers,
Miguel.

_________________
member of the guild of professional dilettantes


Top
 Profile  
 
PostPosted: Wed Feb 28, 2018 8:28 pm 
Offline
Koa
Koa
User avatar

Joined: Mon Jul 27, 2015 8:21 am
Posts: 1223
First name: Brad
Last Name: Combs
Focus: Build
Status: Amateur
I don’t know if it was mentioned already, but cord management was an issue for me early on. I use the SM base and a Dremel. If the cord was hanging down off to the side it could pull the Dremel just slightly. I starting looping the cord through a hook on the ceiling directly above the work area. That helped a lot.

Brad


Sent from my iPhone using Tapatalk

_________________
"Is this the one where I trot downfield and act like I'm lost ?" - Billy Bob



These users thanked the author bcombs510 for the post: pat macaluso (Thu Mar 01, 2018 1:47 am)
Top
 Profile  
 
PostPosted: Wed Feb 28, 2018 8:38 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Fri Dec 14, 2007 3:21 pm
Posts: 2623
Location: Alexandria MN
Not so much about the circle but the smoothness of the cut is the direction of the bit on the outer edges of the channel.

By routing the channel with a separate pass for each edge being sure it was a climb cut towards the outer edge things cleaned up significantly where the cut passes through end grain.

Took me a few years to figure that out. :)

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.



These users thanked the author Terence Kennedy for the post (total 2): pat macaluso (Thu Mar 01, 2018 1:47 am) • bcombs510 (Wed Feb 28, 2018 10:46 pm)
Top
 Profile  
 
PostPosted: Thu Mar 01, 2018 1:48 am 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Sat Jan 31, 2009 8:50 pm
Posts: 1489
Location: Seattle WA
Focus: Build
Status: Semi-pro
Terence Kennedy wrote:
Not so much about the circle but the smoothness of the cut is the direction of the bit on the outer edges of the channel.

By routing the channel with a separate pass for each edge being sure it was a climb cut towards the outer edge things cleaned up significantly where the cut passes through end grain.

Took me a few years to figure that out. :)
So, are you saying, for the final pass on the inside of a ring you would do clockwise and the outside of a ring you would do counterclockwise?


Top
 Profile  
 
PostPosted: Thu Mar 01, 2018 9:30 am 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Fri Dec 14, 2007 3:21 pm
Posts: 2623
Location: Alexandria MN
pat macaluso wrote:
Terence Kennedy wrote:
Not so much about the circle but the smoothness of the cut is the direction of the bit on the outer edges of the channel.

By routing the channel with a separate pass for each edge being sure it was a climb cut towards the outer edge things cleaned up significantly where the cut passes through end grain.

Took me a few years to figure that out. :)
So, are you saying, for the final pass on the inside of a ring you would do clockwise and the outside of a ring you would do counterclockwise?


Yes that is what I do now. It seems like if you go the other way you can get some micro tear out as you enter the area of end grain that can show up as slight irregularities after the rosette is installed.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.



These users thanked the author Terence Kennedy for the post: pat macaluso (Thu Mar 01, 2018 11:17 am)
Top
 Profile  
 
PostPosted: Thu Mar 01, 2018 9:43 am 
Offline
Cocobolo
Cocobolo

Joined: Sat Dec 28, 2013 10:06 am
Posts: 110
First name: Mike
Last Name: Spector
City: ORANGE
State: TX
Zip/Postal Code: 77632
Country: USA
Focus: Build
Status: Amateur
If you have a drill press you might give this a try. They sell for about $20. Just look up "circle cutter"


You do not have the required permissions to view the files attached to this post.


Top
 Profile  
 
PostPosted: Thu Mar 01, 2018 6:57 pm 
Offline
Cocobolo
Cocobolo

Joined: Fri Jan 15, 2016 9:04 pm
Posts: 170
First name: Andy
Status: Semi-pro
Have you used that to make rosette cuts, Mike?

Andy


Top
 Profile  
 
PostPosted: Thu Mar 01, 2018 7:11 pm 
Offline
Cocobolo
Cocobolo

Joined: Sat Dec 28, 2013 10:06 am
Posts: 110
First name: Mike
Last Name: Spector
City: ORANGE
State: TX
Zip/Postal Code: 77632
Country: USA
Focus: Build
Status: Amateur
Yes, I've used it and it works really well as long as you can rig up something to hold the top really flat and steady. It's definitely a "measure twice and cut once" type of tool.


Top
 Profile  
 
PostPosted: Fri Mar 02, 2018 11:35 am 
Offline
Koa
Koa

Joined: Fri Aug 19, 2005 4:02 am
Posts: 1831
Location: The Woodlands, Texas
First name: Barry
Last Name: Daniels
I used circle cutters in the old days to cut rosette rings before jigs were invented;-) You have to modify the cutter so it is cutting a flat bottom slot instead of an angled cut. And it is still a scary operation.

A router in a jig is much better and more flexible.


Top
 Profile  
 
PostPosted: Fri Mar 02, 2018 12:36 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Fri Dec 14, 2007 3:21 pm
Posts: 2623
Location: Alexandria MN
I cut out the sound hole with a circle cutting jig at slow RPM for many years. Now I use the router with a climb cut and the edge is a lot smoother over the end grain.

I think John Greven used a multiple cut adjustable rosette jig that LMI marketed. Not sure if he still is.

Anyone here ever try that tool?

http://www.lmii.com/products/tools-serv ... tte-cutter

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.


Top
 Profile  
 
PostPosted: Sat Mar 03, 2018 12:52 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood
User avatar

Joined: Thu Jan 06, 2011 6:08 pm
Posts: 2678
First name: ernest
Last Name: kleinman
City: lee's summit
State: mo
Zip/Postal Code: 64081
Country: usa
Focus: Build
Status: Professional
Am using lathe tool bits custom cut for the fly cutter .I get the exact width and the depth has about a .005- 015 variance in the depth of cut .Easier to cut my wood veneers oversize, and trim when done.


Top
 Profile  
 
PostPosted: Thu May 03, 2018 7:59 pm 
Offline
Mahogany
Mahogany

Joined: Sun Aug 30, 2009 6:27 pm
Posts: 43
First name: Peter
Last Name: Johnson
Country: Ceridigion, Wales
I would advise taking the first cut at such a shallow depth that it barely scratches the surface. Another tip would be to not hold the router, rather the base itself as low as possible to the work and pull it away from the centre pin throughout each cut.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 27 posts ]  Go to page 1, 2  Next

All times are UTC - 5 hours


Who is online

Users browsing this forum: JoelM, John J, sdsollod and 7 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB® Forum Software © phpBB Group
phpBB customization services by 2by2host.com