iDRY Vacuum Kilns

Sponsors:

Tolerances in frame construction part two

Started by Jim_Rogers, October 17, 2005, 09:14:43 AM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Jim_Rogers

To All:
Recently, the end of last week and over the weekend, I spent several days at the Eastern Conference of the Timber Framers Guild in Burlington, VT.
I went to every seminar on engineering that I could attend.
I listened intently for discussions of tolerances in regard to joinery.
During a presentation by Joe Miller of Yankee Barn Homes, as he was showing his report on peg spacing, size, and joint strength, he discussed his testing of joints with very close tolerances and some sloppy joints.
He found that sloppy joints didn't reduce the strength of the joint, but did reduce the stiffness of the joint.
A gap of the thickness of a business card between the tenon side and the mortise side was discussed as being too large an amount of slop in a joint.
Basically the closer the better, but not to the point where you have to pound the joint together.

It is always important that a tenon that will bear some vertical load be cut so that it will bear on the mortise end fully as possible to prevent crushing of the fibers of either the tenon or mortise when the load is applied.

The spacing of the pegs so that if and when the tenon shrinks that the tenon is not being held up off this bearing surface is important. If the peg should hold the tenon up then it will most likely split the tenon when the load is applied.



One master framer described it to me that when you push a tenon into a mortise you should feel and or hear the air being pushed out of the mortise. It should slide in without pounding and should fit tight to all shoulders.

I brought this info to my friends at the lunch table who believe this high a tolerance is not needed as the wood will shrink any way.

I discussed shrinkage and tolerances with a man well known for his work in taking apart and restoring old buildings.
He stated that the mortise may enlarge with drying and the amount is directly effected by the checking of the surface of the timber toward the boxed heart center. In other words if the check is large then the sides of the mortise can be larger at the surface of the timber due to how wide the check is.
But he said that joints that he takes apart, that have been together for many tens of years, are always tight to the shoulder, possibly due to draw boring, and peg strength.
He agreed that pounding a joint together is bad, and that a business card thickness gap was too much. Because of the shrinkage that may occur. If it's sloppy now, and it shrinks it will be sloppy even more later.

Sloppy joints make a un-stiff frame. That is it could stand up for many years, but unless something else stiffen the frame it could sway in the wind.

It is my opinion based on what I've been taught and read that joints should be tight, not over tight, for a solid and stiff frame.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

ARKANSAWYER



  I will not try to answer the Master question but I have seen some very fine framers and frames.  My GrandPa was a dandy and made the work look effortless. 
   But for peg placement I believe that is very important as well as how a timber will dry.  Most new frames are being built out of vacuum dried timbers cut on a machine with 0.001 tolerance.   Old frames were built out of green material which ment the mortise got bigger and the tenon got smaller and all cut by hand.  The load and stresses must still be considered when making a joint. 
  One thing I have noticed on the old frames taken down the best ones did not have mortises or tenons cut so that they were in the pith of the timber.  Offset to the side was a rule.   Shoulders like you get in squarerule were normal on vertical loaded timbers.  Most pegs were drawbored and of good material that was split out and drawed down to size.

  As for the business card thickness as to loose,that maybe fine for dried machined timbers.  But pounding a joint is not good either.  A tap or two should be fine.
  I build mostly with pretty green stock and believe that there are some differences in how you build with different types of timbers.  But This is a good topic and we can all agree that 1/4 inch is too much.  ;D
ARKANSAWYER

Raphael

  There is a set of proposed definitions and required skill sets for Apprentice, Journeyman, and Master level Timber Framer at the guilds website (http://www.tfguild.org/).
  I think it may be in the members only area as the document is currently under discussion and not in final form.  If I get a chance I'll look for it this evening and try to summarize what makes a "Master", perhaps my new assistant will have a definition as he's just finished Heartwood School's apprenticeship program.
... he was middle aged,
and the truth hit him like a man with no parachute.
--Godley & Creme

Stihl 066, MS 362 C-M & 24+ feet of Logosol M7 mill

Jeff

Derek, Don't know why or what in your history has set you off here, but the previous opinions and information given, were given in a professional, educational and friendly manner. Please do us a favor and do like-wise?  Thank-you.

Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

ARKANSAWYER

 
  Settle for "half-a$$ed" nothing.  Strive for Perfection by all means but never settle for less.  Now I will be the first to say that a frame that does not have all business card tight joints is not junk.  But we should always be shooting for a goal and a high one at that.   When you do very good work you have to pass out very few business cards to keep really busy.  If the Good LORD has given you the gift to work with wood then one should try to always do the very best.  On the other hand we should be very slow to condem someone's work because it is not just like ours.
  What Jim reported was good news.  A little slop is fine in a well engineered joint just know the frame will rack a bit more.  Jim just stated the target to shoot for with the bussiness card.  Perfect joinery takes in the fact of imperfect timbers and makes a thing of beauty.
   Master Framers have brown weathered hands with old scars that hold steel and wood as if it were a new born child.   And have enough good sense to know that "knots" mean not to cut here.


ARKANSAWYER

Joel Eisner

This whole thing of business cards is interesting.  I wish there were tolerances for business cards.  I have stacks of them around laying around from all the meetings I go to and they are different in size.  Even the ones fresh in the box can be differently sized.  Some people like to have odd sized ones that don't fit in the standard clear card pages.  lol

:D

Joel

The saga of our timberframe experience continues at boothemountain.blogspot.com.

beenthere

 ;D ;D ;D
Here I thought they were talking about the thickness of those cards.  Didnt' know it was the width or length.  Am I slow, or what  ???
:)  I never been to a joint that was that loose.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Jim_Rogers

I've been away a few days on a "road job" with my sawmill. I stayed at a motel that didn't have any Internet access so I didn't know that my comments had stirred up a hornet's nests here.

First of all, it was my opinion that this man/ timber framer that I talked to was a "master" as I have seen him on guild raisings, seen him at conferences, seen and/or been taught by him at guild workshops, seen his workmanship, and understand the "tolerances" he tries to instill in us younger/less experienced timber framers.

I am by no means a "master". I am just a timber framer interested in trying to help others by passing on information that I think is interesting and helpful.

Hayton1960 asked in another thread about what level of tolerances we (over here) work toward.

My post "#2" was to reply to his request and make my information available to all, without having to read the entire post or to get lost at the bottom of the older post.

Raphael is correct that the guild is trying to come up with some definitions and tests to help qualify people to these levels of timber framing.

No one is forcing anyone to take any tests. It will be totally up to you whether or not you take one, when they have them all done and available, which could be years down the road.

ARKANSAWYER is right that most old frames do have the joints off center, which is part of "square rule" joinery. This placement of the mortises off center helps to prevent the timber's center check from effecting the width of the mortise (if the mortise was placed in the center).

The use of the term "business card thickness" was again my term for stating a thickness/width of a gap that anyone could easily understand, envision, and use to as a standard. By standard I mean, 1) that's too big or 2) that's ok. I'm not totally sure but I thought a business card was around .020 thousands thick same as a matchbook cover but maybe I'm wrong.

Derek: maybe you can settle for half-assed, but I'm trying to better myself and to help others better themselves. In my opinion, each joint should be better than the last. With experience comes accuracy, with accuracy comes speed.

If these tolerances aren't the level your use to, fine, work your way and we'll work ours. Only your customers will tell you whether or not your level of tolerances are acceptable. If it's fine to them then it's ok. You do your thing and we'll do ours.
Every where people cut frames differently, and no one way is the correct way.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

srjones

FWIW, most of the business cards I have around here measure *exactly* 2.0"x3.5".    In a pinch, one could use to check 2" mortices?   ???

I think what Derek might be getting at is a perception that timberframing must be "tight" (clean, precise, etc.) in order to be worthwhile and worthy of respect.  If the only the only good joint is a perfect joint, then you might as well send it through a Hundegger.   

In my humble opinion, (and as stated by others) it should be up to both the builder (producer) and the customer (consumer) to determine what is acceptable aestheticaly, as long as safety is not compromised.  A qualified structural engineer or building inspector should determine what is structural safe.

So really, as we discuss this, we're talking about two completely different things:  Looks and safety.

As far as aesthectics go, let's think about this for a minute:  if you have season checks in your timbers that often are 1/8" in the middle and can be up to 1/4", what's really the harm in having 1/16" or even 3/32" gaps around the shoulders?  In fact, it might look a little odd if there wasn't a little gap.  BTW, my personal preference is about 2-3 business cards worth of a gap on each side of the joint.   Also, how big are the timbers that are being joined?  To me, the bigger timber, the more acceptable it would be to have a larger gap.  Finally, how close to view and touch is the joint?  Is your 18 month old toddler going to get her finger stuck in it if she can reach it?  (about 1/4" would do it, and yeah, that's probably too much).  But are you going to notice that same gap at the peak of a pair of rafters more than 20' straight up?  Probably not...

I agree, though, that a joint shouldn't be so sloppy that it's vulnerable to failing.  However, I'm trying to figure out how that could happen, and the only way I figure is by racking, which should be prevented by bracing or sheathing.  Maybe in tension joinery?  No, that's held by the pegging.  I'd be really interested to hear about a joint that was so poorly made (not poorly designed) that it failed.

Bottom line.  Wood is imperfect, people are imperfect.  Strive to do good work with the imperfections you're given.  Leave the perfection stuff to the furniture and cabinet makers.

Have a good weekend everyone.

-srj


Everyone has hobbies...I hope to live in mine someday.

Jeff

BADMOJO, I dont recall ever having anything to do with you until now. If I did, I was doing my job. If you have issues with me, I suspect you better let me know in private as this is my turf, but  maybe we can work them out. As for maybe "Lets see if this one gets through will get through", is  uncalled for because nothing was here was deleted or edited by me.  Just remember, this is a private forum that the public is allowed. You have to register and be accepted to post. Attitudes towards the moderator here is not acceptable.
Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

Jeff

Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

mark davidson

here's 2 more cents...
a master is someone who's done trying to be a master....
whatever you are striving for is in your hands, whether it's .01 or .25
there are folks who love either tolerance level....
in my area the 2 extremes are easy enough to find.
in the .001 category, a CNC log/timberframe shop is 4 miles away from me(they kicked in about a year after I left the family farm to go back to timberframing -3yrs ago) At first I was poo-pooing this shop which seemed to take forever to make a frame. Now they have a model home out front which I like quite a bit, and they've sold some frames locally I would have loved to build......
in the .25 category was my cousin's barn, which was dismantled last year. built in 1850/60, the barn had it's roof ripped off by a hurricane in the 1950's, but stood square till the end and was every bit as beautiful as the CNC model. once I had the joins apart I saw tenons a full half inch smaller than the mortices everywhere.... it was a good lesson in the strength of a timberframe, even with sloppy joints.

if you need to be recognized as a master to the whole world, then I would look to the timberframer's guild, the carpenters fellowship, and other similar groups, they are quite focused on the craft and probably would have the most respect in the rest of the world.

Jim Haslip


Strive for perfection and you will rarely be disappointed.

Regards, Jim H.

Gabel Holder

Great topic all.

For me, tolerances vary from job to job and from joint to joint but pretty much are governed by the following things in the following order.

1.  The work the specific joint is doing.  As a carpenter, I must build it strong enough or I am a failure.  This requires a  sound understanding of what the load is and what is required of the joint.  I have seen people make tight shoulders on joints that are in tension, but only use a 4" tenon and 1 peg.  Would have been better to make a longer tenon and more pegs and have a gap at the shoulder. 

2.  The project (and the client).  Am I building a church or other public building meant to inspire or am I building a working barn for a farmer who doesn't need or want perfection even if he could afford it?  Seems he is better served by me spending my time building his barn efficiently rather than trying to get the hidden, structurally unnecesary abutments to perfectly kiss each other.  Client expectations, budget, intended use of the building:  these are a few things that come into play here.

3.  The materials being used.  Is it dry reclaimed timber (which more or less stays where you put it) or green oak (which I have seen shrink 1/2" in width across an  8" face in 1 year.)

4.  Location of the joint.  Is it eye level right inside the front door or is it in the closet or is it 35' up in the air on the upper side of a timber.  A friend of mine who is a good carpenter and timber framer told me that the most important joints to have "dollar bill tight" are the ones in the bathroom on the opposite wall from the toilet.  He says they get the most scrutiny.

As a carpenter, I see it as my job to make it tight where it matters and make it fit where it doesn't.

But like several have said -- a quarter is probably too much.

Keep it coming, this is fun,

Gabel


Raphael

We got all the bells and whistles here.
  In fact I was noticing that little pink icon below your handle.
Didn't remove some important body parts while disassembling the boat did you?
... he was middle aged,
and the truth hit him like a man with no parachute.
--Godley & Creme

Stihl 066, MS 362 C-M & 24+ feet of Logosol M7 mill

Stumpkin

Great topic , lots of good discussion. I'm glad I found this forum. 8) I feel right at home with all the familiar names on the left side of the page. Jim, looks like you've put a lot of time in here, thanks for all your hard work. Tom
"Do we know what we're doing and why?"
"No"
"Do we care?"
"We'll work it all out as we go along. Let our practice form our doctrine, thus assuring precise theoretical coherence."      Ed Abbey

Raphael

Hey Tom, welcome to the FF!

Now that you know where we are, pull up a timber (have a slice of pizza ;)) and set a while.
... he was middle aged,
and the truth hit him like a man with no parachute.
--Godley & Creme

Stihl 066, MS 362 C-M & 24+ feet of Logosol M7 mill

jmaine

This is an interesting discussion. I live in an old timberframe house (built around 1800) and the tolerances are not even close to the thickness of a business card.   The gaps in the some of the joinery are large, in some cases nearly an inch. I think many timber framers today would survey the joinery in my house and consider it second rate, a total hack job.   However, the building has stood the test of time. When we purchased the building, it had to be moved ½ mile down the road and through a field to the new site.  Very little damage was done, we took pictures before an after the move and there really wasn't any significant damage.  The original plaster walls/ceilings were still intact with very little movement or cracking.  I think the house was overbuilt which helped, but I wonder if modern timberframers pay too much attention to exacting tolerances, perfect fits, etc?  Is the cost to obtain the perfect fit worth the effort?  I built a 12' x 16' shed (from Jack Sobon's book) and plan to build a barn this summer.  I was very careful in cutting my shed frame and the joinery is tight.  Although, I wondered if the extra time I spent getting the joinery so tight really made much of a difference. Could I have cut the frame in half the time if I wasn't so fussy?  Maybe ¾ of the time?  I don't know.  I've done some work with some other timberframers and they've all seem to strive for the "perfect joint"; shaving off 1/32 of inch at a time, constantly checking their measurements, etc. Maybe a good strategy is to spend extra time on the more critical joinery and not be as fussy on the remaining joinery?  I wonder what a timberframe master from 200 years ago would say if he was able to work with a modern timberframer?  "Wow, that is some tight joinery, very impressive.  However, it's taking forever.  I don't have time for this, we need to get this frame up before my cows die of exposure."

Maybe the priorities are different now? Perhaps in the old days the top priority was building an affordable structure in a reasonable amount of time?  It could be that cost isn't as much of an issue anymore?  Would there be more timerframe buildings around if it wasn't so expensive?  I sometimes wonder if the obsession with super tight joinery drives up the cost of a timber frame home which is why more people don't opt for a timberframe?  I certainly don't know the answers to these questions, but wonder what others think.   

Joe

Raphael

  Historically the timber frame in a house was hidden behind the walls so there was no aesthetic reason for making the joints ultra tight especially on the non-reference faces.  Also bear in mind when you look at a large gap in an old frame that a good deal of that gapping appeared after the joint was cut and assembled for several years.  The timbers shrank, settled, twisted and checked.

  I'd have to ask someone who's surveyed a lot of old frames to be sure but I'm guessing tolerences in barns were actually closer than in houses back then as barns are subject to more extreme loading.

  The cost of a frame is going vary considerably depending on what you're buying and who you're buying it from; general appearence and engineering are going to drive the price as much as joint count.

  Based on my conversations with Jack Sobon at the start of my house project, what I've cut would cost ~$45k if he'd done it.  That's working out to only 15% of the cost of the house (right at the low end of the spectrum).  I'm guessing it have been more like $90k from Tedd Benson; who's frames are cut on a Hundegger, planed, chamfered, oiled and featured in Fine Homes.  Both of these guys are going to produce mighty tight looking joints fast.

  IMHO the process you describe of taking a 32nd at at time and remeasuring doesn't really exist in a professional timber frame shop.  I started out that way and as my confidence in myself and my tools increased things changed, I suspect you're about half a shed away from seeing this yourself.  Picking the stick and layout is always going to be a big consumer of time and a some of the difference in cost between stick built and timber frame is right there.

  Another big expence has to do with finishing.  There's tons of cheap standardised hardware for wiring and plumbing a stick built house so every challenge has a premade solution.  Unless your electrician is well versed in wiring a timber frame you're going to wind up paying him to stop and think the process through as he goes.
... he was middle aged,
and the truth hit him like a man with no parachute.
--Godley & Creme

Stihl 066, MS 362 C-M & 24+ feet of Logosol M7 mill

Thehardway

Wow, what a topic.  I've seen joints in timberframes that are not even close to business card thickness tolerance as they were on the wrong side of the timber!  How many of you would use a timber that had a miscut joint for "character" vs. scrapping it or cutting it down and reuseing it for a smaller member?

I have seen quite a few joints that were cut two big and the slop was taken up by shims or wedges.  I believe one famous "master" even advocates cutting rafter to purlin dovetail joints lose and then wedging them so that as the timber shrinks the wedge keeps falling in and thereby keeps it "tight".

In many cases I thought the purpose of a housed tenon was to conceal gaps in the joint as the timbers shrunk.

I think part of this discussion goes to whether the frame is owner built or professionally built.  I am a bit of a perfectionist myself but will live with some errors in exchange for time with my family or fishing or  some extra $ in my pocket vs. paying a "professional".  What really racks my frame is when I pay a "professional" to do a job because I doubt my own skill level and then he performs the work in a manner or timeframe that I could have done myself for free.   I have been burned by mechanics this way quite a bit recently. What is worst is professionals hiding mistakes.  I would rather have them tell me or leave it out in the open (enter the mortice on the wrong side of the timber) as a testimony to the fact that they are human and make mistakes than try to cover it up

Some of the historic frames we look at were homemade, others were built by the local jack of all trades and some were actually built by masters.  All are still standing and witness to the inherent sturdiness and superiority of the timberframing element.

Bottom line,  do work that you are proud to put your name on and charge what you feel is commensurate with the work you perform and throw in a little extra for good measure and love of the craft and no one will prabably fault you.  Throw it together quick to add a few dollars to the bottom line and get an extra day of fishing on the customers dollar and now you might have a problem.

At this point I work for myself and the pay I receive is the beauty of my own work.  I couldn't afford it any other way.
Norwood LM2000 24HP w/28' bed, Hudson Oscar 18" 32' bed, Woodmaster 718 planer,  Kubota L185D, Stihl 029, Husqvarna 550XP

Raphael

Quote from: Thehardway on January 12, 2007, 08:28:23 AM
Wow, what a topic.  I've seen joints in timberframes that are not even close to business card thickness tolerance as they were on the wrong side of the timber!  How many of you would use a timber that had a miscut joint for "character" vs. scrapping it or cutting it down and reuseing it for a smaller member?
<snip>
At this point I work for myself and the pay I receive is the beauty of my own work.  I couldn't afford it any other way.

Beauty is in the eye of the beholder, I happen to like this look.


  This was a braced Spruce girt from the 14' bay that got replaced with Oak and repurposed as an unbraced girt in the 8' bay, I have two of these in my frame.  For myself I'll use a timber as planned if the error doesn't compromise it's strength.  Thanks to the fellow who cut my primary frame (and his father) I have many examples.  The most glaring error doesn't show, it's an entire series of joist pockets that are now against an outside wall and buried under flooring.

Here is a misscut brace mortice in a tie beam, I have eight of these complete with peg holes:

Unfortunately these will be covered by the ceiling.

He also seems to have got a bit confused measuring for middle most attic floor joist:


This last pair isn't really a cutting error, they result from differences in my floor plan vs. his.  This drop in joist mortice will remain open and visible above the landing on the main staircase.


It's opposite number gets buried below the top tread of the staircase.


None of this would be acceptable in a frame I intended to sell but are fine for a frame I purchased at ~1/3 of it's estimated value.  My own work has been a bit more anal, but there are a couple minor adaptations.
... he was middle aged,
and the truth hit him like a man with no parachute.
--Godley & Creme

Stihl 066, MS 362 C-M & 24+ feet of Logosol M7 mill

Jim_Rogers

Quotean entire series of joist pockets that are now against an outside wall ........

When that happens at the school in Maine, they say that's for the addition to be built later......... ;D :D

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Thank You Sponsors!