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Nov 14, 2017 - 7:32:28 PM
319 posts
Joined Jul 10, 2012

I am experimenting with steam bending and just finished putting together some mandrel blanks for the various lamination diameters to trim down on my lathe. My plan is to steam three 1/4" slats, wrap each of them around a mandrel and then fit them inside a mold ala Ken LeVan's approach, among many others. I'm looking for a snap fit within the final mold, so I figure that each 1/4" thick lamination would require a mandrel about 1/2" smaller than the one before it as you move inward to get the diameter tight. I'm curious if this approach fits the experience of folks with a bit more experience than me. So, here is my set of diameters:

11" Rim using a 11 1/8" (outer diameter) mold
1st mandrel = 10 5/8"
2nd mandrel = 10 1/8"
3rd mandrel = 9 5/8"

12" Rim using a 12 1/8" (outer diameter) mold
1st mandrel = 11 5/8"
2nd mandrel = 11 1/8"
3rd mandrel = 10 5/8"

Thanks in advance!

David

Nov 15, 2017 - 6:19:42 AM

RB4picker Players Union Member

USA

1160 posts
Joined Jul 15, 2011

Been thinking about similar stuff.
That would, on 11" rim, give you 1/16" over to play with.
Also, will you butt join the ends of each slat or cut somehow on a long taper so it overlaps for a stronger, less obvious joint?
David

Nov 15, 2017 - 7:25:43 AM

319 posts
Joined Jul 10, 2012

quote:
Originally posted by RB4picker

Been thinking about similar stuff.
That would, on 11" rim, give you 1/16" over to play with.
Also, will you butt join the ends of each slat or cut somehow on a long taper so it overlaps for a stronger, less obvious joint?
David


I suppose that making the mold to 11 1/4" would be a bit safer to give me 1/8" to play with instead of only 1/16... I have been waffling on the joint question, actually, leaning toward butt joints, though either would work with this approach and there are advantages to both.  I've also considered using a butt joint for the outer and middle layers, which will have hidden joints, and a scarf joint for the outer layer to get the butt joint advantage of not having to wait for each lamination to dry and be sanded before adding the next layer and the scarf joint advantage of a predictably less obvious joint for the visible joint.  

David 

Nov 15, 2017 - 10:26:58 AM

RB4picker Players Union Member

USA

1160 posts
Joined Jul 15, 2011

David,
Just to be clear, I haven't built rims yet, just thinking.

I don't know if 1/16" is enough or not. But if you go over an eight all way round (11 1/4") and then turn it back to eleven even, your outer slat is only 1/8" thick then.
Others will prob chime in here but I was thinking maybe inner and middle slat at 1/4" and outer slat at 3/8" and 11 1/4" outer dia. This would turn back down to 11" and still leave 1/4" outer slat.

I may be over thinking this though. A 1/16" over may work fine.

I was wondering mostly about how you make the scarf cut. Any ideas?
David

Nov 15, 2017 - 11:15:20 AM

319 posts
Joined Jul 10, 2012

I've seen a few methods for making the scarf cut using a table saw, belt sander, and a router. The table saw was pretty straight forward, line the slat up on its side and slide through at an angle. The belt sander is pretty clear as well, though I think using a backing jig to ease the piece in evenly would be crucial. The router method was quite cool. You take the slat and lay it along a support set at an angle, then feed the end of the slat over the router so the angled cut is made on the underside of the slat.

All things considered, I will likely go with the belt sander method.

David

Nov 15, 2017 - 12:02:44 PM

rudy Players Union Member

USA

11360 posts
Joined Mar 27, 2004

David, Before you get to heavily involved in the process you might want to check out recent posts I've done with guides for rim construction.  My stuff is specifically tailored to be easy to do, so consider that.

Making a rim form:

https://www.banjohangout.org/archive/331300

Using this method you end up producing a rim that requires no turning and fits commercially produced heads with minimal finish sanding of the outer rim surface.

"Goldilocks" rim laminations:

https://www.banjohangout.org/archive/330189

Details how to make perfectly sized laminations and how to make a nearly invisible lap joint for the seams, no length calculation necessary.

Both of those rim making topics are companion pieces for the "Easiest, Cheapest, Fastest Steam Cabinet" topic:

https://www.banjohangout.org/archive/329951

My personal thoughts on the rim laminations is that I see no need to make butt joints that will be virtually assured of having a gap when you clamp them up to be glued.  Why introduce even a small gap when it's so easy to do gapless lap joints?  Part of the entire process of making a rim should be doing it in a manner that assures the greatest integrity.

I see a huge benefit to any method that can be done and not involve lathe turning, too.  If you're doing turned rim resonator banjos then you have to go a different direction, but if you're doing open backs then consider the alternatives to laborous and difficult processes that are prone to higher probability of error.

As a side note, all the photos are there, but these topics got radically screwed up when the topics were archived.  I'm close to giving up on the "New and Improved" Banjo Hangout format, as there's nothing I can count on any longer to look like what was originally presented.

Edited by - rudy on 11/15/2017 12:06:13

Nov 15, 2017 - 12:48:39 PM

319 posts
Joined Jul 10, 2012

quote:
Originally posted by rudy

David, Before you get to heavily involved in the process you might want to check out recent posts I've done with guides for rim construction.  My stuff is specifically tailored to be easy to do, so consider that....

 


Rudy.  I have had an archive of your posts on my computer called "Guidance from Rudy" for years.  That said, it is nice to have these links all in one place and I have your plan for making a rim form already printed in my shop for next week.  I have made a good number of block rims with a router, but honestly, I am interested in the challenge of laminated rims and lathe work as much as I am in having the rims.  Also, I hear you on the scarf joint advantage and will be experimenting with both, keep you posted!  

By the by, any thoughts on the other David's question about the cleanest method of making a scarf joint?    

Nov 15, 2017 - 2:26:55 PM

RB4picker Players Union Member

USA

1160 posts
Joined Jul 15, 2011

Thanks much Rudy.

Nov 15, 2017 - 2:53:11 PM

rudy Players Union Member

USA

11360 posts
Joined Mar 27, 2004

quote:
Originally posted by dpgetman
quote:
Originally posted by rudy

David, Before you get to heavily involved in the process you might want to check out recent posts I've done with guides for rim construction.  My stuff is specifically tailored to be easy to do, so consider that....

 


Rudy.  I have had an archive of your posts on my computer called "Guidance from Rudy" for years.  That said, it is nice to have these links all in one place and I have your plan for making a rim form already printed in my shop for next week.  I have made a good number of block rims with a router, but honestly, I am interested in the challenge of laminated rims and lathe work as much as I am in having the rims.  Also, I hear you on the scarf joint advantage and will be experimenting with both, keep you posted!  

By the by, any thoughts on the other David's question about the cleanest method of making a scarf joint?    


Yes.

Since scarf joints and lap joints are essentially the same thing, you're probably going to be hard-pressed to find a more perfect, stronger, or less visible scarf / lap joint then what I demonstrate in the "Goldilocks Rim Laminations" link I posted above.

I think you'd most likely agree that the rim below isn't too shabby in the scarf joint department.  It's shown immediately after sanding the lapped joint with a vertical oscillating spindle sander and then truing up the edge with a pass under the Safe-T-Planer, no sanding to pretty it up.  That particular rim is 5 layers approximately .010" in thickness to make a 1/2" wall rim.

Nov 16, 2017 - 9:56:32 AM

Ken LeVan Players Union Member

USA

10187 posts
Joined Jun 29, 2005

quote:
Originally posted by dpgetman

I am experimenting with steam bending and just finished putting together some mandrel blanks for the various lamination diameters to trim down on my lathe. My plan is to steam three 1/4" slats, wrap each of them around a mandrel and then fit them inside a mold ala Ken LeVan's approach, among many others. I'm looking for a snap fit within the final mold, so I figure that each 1/4" thick lamination would require a mandrel about 1/2" smaller than the one before it as you move inward to get the diameter tight. I'm curious if this approach fits the experience of folks with a bit more experience than me. So, here is my set of diameters:
 


Whenever I see my name mentioned as a source of advice, I get a little nervous about what advice I might have given.  I hope I never suggested that when I laminate a rim, the layers "snap into place".  That couldn't be farther from the truth. 

I make rims in the 5/8" Ø range and the outer layer I use is close to 1/4" - I would not characterize them as "snapping into place" - Being forced into submission while kicking and screaming is more accurate. Sometimes I use 15 clamps on one lamination - I have good cauls, too. I think the hairy chested boys have hydraulic systems to do this.

Below is a picture of 4 rims going at once - two 11" ones and one 12" one the rim on the top in the background is getting a thin 1/8" veneer glued in and even that is taking at least 10 clamps. The eerie red glow is a heat lamp above.

 

The other thing to keep in mind is that wood is a loose-goosey organic material and when you steam it it's going to cup and do other things, so it's best to glue and clamp it into the form while it's still pliable and can be forced into conformance - you need to see the glue squeezing out of the joint top and bottom. 

If you make the slats in advance, as you are contemplating, then once they dry and take a set, you have to dress them to get the sides straight so you get a good glue contact. You also have to dress the scarf joint before gluing on the next layer,so I would recommend giving the thickness enough leeway to allow for that.  I put the whole 3-ply rim on the lathe and true the inside before gluing in the 1/8" veneer.

Edited by - Ken LeVan on 11/16/2017 09:58:07

Nov 16, 2017 - 10:16:42 AM

rudy Players Union Member

USA

11360 posts
Joined Mar 27, 2004

Ken sez:

"I make rims in the 5/8" Ø range and the outer layer I use is close to 1/4" - I would not characterize them as "snapping into place" - Being forced into submission while kicking and screaming is more accurate. Sometimes I use 15 clamps on one lamination - I have good cauls, too. I think the hairy chested boys have hydraulic systems to do this."

******************************************

I like that!  Finding that ideal range where laminations conform relatively easily without brute force is what the Goldilocks topic was all about.  I personally believe that rims that aren't holding excessive static energy are much more reactive to energy imposed by the stimulation of the structure by the energy imposed by the strings.  For me it results from lam thickness of something in the order of .010".  Thin enough to bend easily, especially when subjected to a few minutes of steam, but thick enough to allow it to be machined to meet my needs.

I think that may have subconsciously been the rationale behind block rims, although it may have just as easily been pure economics or the ability for less skilled workers to produce rims that were reliable and that would stay together.

Edited by - rudy on 11/16/2017 10:19:35

Nov 16, 2017 - 12:43:59 PM

319 posts
Joined Jul 10, 2012

Thanks fellas,
I was thinking that I could pre-soak the slats, steam them one at a time, and wrap them around the mandrels with a compression strap one at a time and leave them to cool. If the compression strap won't keep the slat from cupping while it cools, then I see the advantage of working the slats into the mold while they are still pliable, but I guess that would mean doing one slat at a time (steaming, wrapping, inserting into mold, gluing, drying, sanding, repeat).
David



Tagged: rudy ; Ken LeVan

Nov 16, 2017 - 1:41:51 PM
likes this

Ken LeVan Players Union Member

USA

10187 posts
Joined Jun 29, 2005

quote:
Originally posted by rudy

Ken sez:

"I make rims in the 5/8" Ø range and the outer layer I use is close to 1/4" - I would not characterize them as "snapping into place" - Being forced into submission while kicking and screaming is more accurate. Sometimes I use 15 clamps on one lamination - I have good cauls, too. I think the hairy chested boys have hydraulic systems to do this."

******************************************

I like that!  Finding that ideal range where laminations conform relatively easily without brute force is what the Goldilocks topic was all about.  I personally believe that rims that aren't holding excessive static energy are much more reactive to energy imposed by the stimulation of the structure by the energy imposed by the strings.  For me it results from lam thickness of something in the order of .010".  Thin enough to bend easily, especially when subjected to a few minutes of steam, but thick enough to allow it to be machined to meet my needs.

I think that may have subconsciously been the rationale behind block rims, although it may have just as easily been pure economics or the ability for less skilled workers to produce rims that were reliable and that would stay together.


Rudy, I was going to mention that if your rims are "Goldiliocks", my three plies are the three bears.

Having said that, you are losing me with the "holding static energy thing"- (respectfully) I think that's a handy justification for using .100 slats.  I LOVE the old Vega 7 ply rims, don't get me wrong, but they aren't under any more or less stress than 3 ply ones once they stabilize - just easier to make.  Once the slats are glued against one another with a no-creep glue and the glue cures, they stabilize and are in equilibrium. If I was to cut one of the slats out with a bandsaw it would not spring open.  The tendency of a piece of wood to stabilize once steamed and laminated is not a function of thickness. 

In terms of stabilizing at the new configuration, look at a laminated archery bow - once it is formed by forcing it and gluing it into the desired shape, it remains at that "set" and will always spring back to its laminated form which is its new equilibrium, and with a large amount of force - it does not attempt to straighten itself.

Nov 16, 2017 - 3:50:58 PM

rudy Players Union Member

USA

11360 posts
Joined Mar 27, 2004

quote:
Originally posted by Ken LeVan
quote:
Originally posted by rudy

Ken sez:

"I make rims in the 5/8" Ø range and the outer layer I use is close to 1/4" - I would not characterize them as "snapping into place" - Being forced into submission while kicking and screaming is more accurate. Sometimes I use 15 clamps on one lamination - I have good cauls, too. I think the hairy chested boys have hydraulic systems to do this."

******************************************

I like that!  Finding that ideal range where laminations conform relatively easily without brute force is what the Goldilocks topic was all about.  I personally believe that rims that aren't holding excessive static energy are much more reactive to energy imposed by the stimulation of the structure by the energy imposed by the strings.  For me it results from lam thickness of something in the order of .010".  Thin enough to bend easily, especially when subjected to a few minutes of steam, but thick enough to allow it to be machined to meet my needs.

I think that may have subconsciously been the rationale behind block rims, although it may have just as easily been pure economics or the ability for less skilled workers to produce rims that were reliable and that would stay together.


Rudy, I was going to mention that if your rims are "Goldiliocks", my three plies are the three bears.

Having said that, you are losing me with the "holding static energy thing"- (respectfully) I think that's a handy justification for using .100 slats.  I LOVE the old Vega 7 ply rims, don't get me wrong, but they aren't under any more or less stress than 3 ply ones once they stabilize - just easier to make.  Once the slats are glued against one another with a no-creep glue and the glue cures, they stabilize and are in equilibrium. If I was to cut one of the slats out with a bandsaw it would not spring open.  The tendency of a piece of wood to stabilize once steamed and laminated is not a function of thickness. 

In terms of stabilizing at the new configuration, look at a laminated archery bow - once it is formed by forcing it and gluing it into the desired shape, it remains at that "set" and will always spring back to its laminated form which is its new equilibrium, and with a large amount of force - it does not attempt to straighten itself.


Thank you for the "respectfully" you included, we're usually not far off the same mark as far as our opinions on construction details.

Much as we'd all love to solidly believe the idea that a rim will remain without any changes after it's glued the simple truth is there are a lot of examples of rims that have experienced delamination for various reasons.  I'll guarantee you that the less "brute force" that has to be applied during the bending and lamination process the better the chances that the rim will not experience fatigue stress fractures along the glue lines years from now.

That's where the static energy comes into play.  I've yet to see any lamination that didn't naturally want to straighten over time; the tree knows how it was originally meant to be aligned and always wants to return to that form.  I don't think it's anything beyond simple logic that serves as adequate explanation for that.

As a "thought experiment" (the kind Albert Einstein was so fond of...) simply envision bending two stacks of laminations 36" in length into a simple circle.  One of them would be comprised of 3 pieces of 1/4" thick wood, the other 12 pieces of veneer 1/16" in thickness.  I'll again offer my money-back guarantee relating to which one is more easily accomplished.  After doing that if you don't understand the concept of static energy I can't offer any further explanation.

I'm all for a "kinder, more gentle" type of rim build-up, and I'd like to think of myself more as a "Rim Whisperer" than a "Rim Enforcer". smiley

I should NOT post while sipping fairly large quantities of High Valley 2014 Cabernet before dinner...  wink 

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