Wednesday, March 1, 2017

A Ming-Inspired Cabinet (87)

When I left off last time I had described some of the difficulties I was facing drilling well-aligned holes in the bifold door hinge stiles. Due to problems that cropped up using the right angle attachment on the milling machine, which would not hold alignment due to starting torque from the motor kicking it out, I had to scrap the original hinge stiles and make 4 new ones, cutting up a precious 4x8" bubinga beam in the process. That was my last stick of bubinga of any decent size.

In an effort to stabilize the angle attachment, I put together a plywood gusset and some various blocks to connect it to the column of the mill.

Here's a look at the arrangement once again:





With considerable fiddling I was able to achieve near-perfect alignment over 5" travel:



 Alas, after countless test start of the motor and rechecks and realignments - i'm talking hours of time here- I was forced to conclude that the gusset wasn't providing adequate reinforcement.

A reader wrote to me and suggested that a culprit in all of this might be the quill itself, which, due to wear, might be permitting a degree of rotational movement. I was skeptical, as the quill seemed tight in travel if anything, however later examination where I used the leverage afforded by the right angle head, showed that there was in fact slop in the quill. A new and interesting fact to learn.

The quill does have a locking mechanism in the head, however the lock gets stuck once clamped and has to be disassembled to get the quill moving again - a bit of a PITA - so I have been making no use of it. With the awareness however that quill movement in rotation may be a factor, I tightened it up to lock the quill.

After sleeping on it, I returned to the shop today and decided to try remaking the gusset again, only beefier. I wanted it as stiff as possible using what i had on hand, namely a few bits of plywood and various hardwood offcuts.

Here's the 'MARK II':
 

The wood-to-wood connections are screwed and bolted together, but I leave the clamps in there for extra reinforcement:


The plywood connects by way of a pair of Canarywood angled blocks to the sliding dovetail under the ram:


Perhaps the biggest weakness in the entire contraption is the connection to the RA head, which is hardly what one would call a perfect surface. It is also a short surface. i considered bolting metal to it, but I just couldn't quite bring myself to do that.

I detected some play in the connection so I added some copper shims each side in a bid to rectify the problem:


As it turned out, the 'Mark II' did offer some improvement, however there still was play, and the the start-up torque simply would find whatever tiny avenue of slop there was in the connections and exploit it. Drilling each hole was a painstaking process of drilling, then re-tramming the mill before the next cut. In this way, while I could not completely eliminate a bit of drift with the RA head, I could keep it to a minimum.

As before, I commenced work putting in the 5/16" x 18 TPI self-tapping inserts. I used a 7/16" (0.4375", 11.11mm) Whiteside end mill to bore out in one go:


I find Whiteside router bits to be more accurate dimensionally than Freud.

In goes the insert, using the shop-made tool:


Done:


Connecting to these inserts are hardened steel pins, originally shouldered bolts, which have had Allen  heads burned into them using EDM technology, a task performed by my local machine shop:


In:


The hardened pins in turn slip into Oilite® plain flanged bearings:


The bearings will mount in the cornice beam atop the cabinet, the lower framing member in the bonnet.

All four tops done:


A good while later, at long last, the lower brass pivot pins were fitted as well:


Golly. What an ordeal that was. "Just need to drill 8 holes" - sounds so simple, and it is a simple task in one sense. But it was one of the trickiest aspects to the entire build so far and I took a beating getting it done. Very frustrating at times. After being sick for a month, and then this setback with the stiles, I am about 6 weeks behind schedule, which is stressing me out a bit, and that hasn't helped any.

Moving forward, the RA attachment clearly is not ready for prime time. Also, a few days ago it seized up while making test starts. I got it freed up again and lubed it a bit, but it probably needs a rebuild from what I can tell. A least a look-see inside. Likewise, the main head of the mill needs a rebuild. I've realized this for a while, given the stiff quill movement and sticking (useless) quill lock, and now I can add to the mix the slop in the quill has rotationally. I'd also like to change from the current tool holding set up with a collet nut and convert to a overhead air-powered drawbar set up to hold tooling. Hopefully his year I'll be able to tackle that project - at least in terms of getting it going. A specialist spindle rebuilder will be needed to put the unit right.

As for the hinge stiles, I still have some catching up to do in terms of cutting mortises for the battens, and dadoes for the panels. I'm planning to knock most of that off with another shop session, however I'll omit taking pictures since it is a repetition of earlier work. Within a few days I should be able to put some doors together, so that work will form the subject matter of the next entry in this series.

Thanks for visiting the Carpentry Way.

26 comments:

  1. Awesome work Chris!

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  2. Phew!! Another problem solved.
    I've always believed that life is just a series of problems, and that when there are no problems, you're done living. I'm always looking forward to the next problem.

    Now, a couple of questions ... because I anticipate building a small replica of a Ming cabinet, about the size of a bed table ... and I've waited 87 episodes to see how you hang the doors. :)

    1. Why have you chosen hardened steel hinge pins for the top and brass for the bottom? I imagine a wear factor is involved.

    2. From your research, (yes, I've done some, but the few books left to us are thin on this subject), how, and of what materials, were these pins and pivot points fabricated in the actual Ming era?

    Thanks Chris, for these postings. While I'll never strive for the level of .00001" accuracy that you work to, I certainly appreciate seeing how you solve problems.
    --
    Bob Easton

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    1. Bob,

      thanks for the comment and questions.

      I could have gone with brass for the long upper pins, however given that the pin threads in and out by way of a fairly small allen head drive, I worried that over time and possible removals and reinstalls it might not stand up as well as a steel one. Also, the shouldered bolt which became the pin necks down at the bottom before the threads start, and that is the weakest part. I wonder if it were brass if it would be adequately strong in that area?

      As for (2), with Ming furniture you'll se two type of hinging systems. By the late Ming, metal leaf hinges were common, while in the earlier Ming period it was more common to see doors pivot on their stiles. I've taken inspiration from this earlier system, which is entirely derived from Chinese architecture. In these types of of door, the hinge stile is extended top and bottom and pivots are formed directly upon the wood. The framing above and below the door then has some blocks added, projecting frontward, which house the stile's wooden pins.

      I considered briefly doing all-wooden pins, using lignum vitae for both pins and bushings, however i decided to go with metal later on.

      The biggest defect with Chinese furniture doors, whether hinged with metal or wood mechanisms, is that the doors can only open 180˚ before the door itself runs into the surrounding frame. I've never liked this and the fact that the door is stopped by direct contact with the frame both creates a wear area and the door is vulnerable to accidental damage if someone walks into it when in the opened position.

      I borrowed the idea of modern knife hinges in moving the door pivot point forward and out, so as to allow the door to swing 270˚. I took the archaic form of Chinese door hinge and modernized it by making the stile L-shaped and using metal parts for the wear areas so as to give it better functionality. Also, if any of the meal parts were to wear out, they are simple in form and could be replaced by any competent machinist.

      ~C

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    2. THANKS Chris!
      I thought the early pins were wood, but couldn't tell for certain. Thanks for the clarity and the rationale for your current version. Very much appreciated.
      -- Bob

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  3. Holy moly, impressive perseverance! Nothing is worse than unknown/unpredictable sources of variability. I got empathy tight stomach while reading. And impressive fixtures, very slick. Those doors will swing for millennia. Thanks for letting us watch and learn.

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    Replies
    1. Jamie,

      very kind of you to say. I'm just relieved to have gotten through this stage.

      ~C

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  4. Nice work Chris! Sorry to hear that it's been such an episode, certainly frustrating when a "simple" task turns into a very long and complicated ordeal.

    A very nice solution to the issue of wearing wooden parts in this case.

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    Replies
    1. Bian,

      a pleasure to receive your comment, appreciate that you like the solution I came up with for the hingeing.

      ~C

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  5. Struggle is what defines life, and man, it seems like you've had a lotta life this past month! The dedication and finesse you put into just drilling a hole...it definitely is a pinnacle of craftsmanship to look up to.

    An aside- what tracks did the machine shop use to make the allen heads? Some early Daft Punk stuff, or maybe something more like Porter Robinson?

    Thanks for keeping up the posts and letting us have a window to view your process by!

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    Replies
    1. Steven,

      your middle paragraph gave me pause, until I realized, ah, yes, 'EDM' has another meaning, likely a more commonly understood one: Electronic Dance Music. Of course. I can't speculate on the shop's music choices, but the Electrical Discharge Machining they do is pretty cool. I think I prefer it to the other EDM generally.

      ~C

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  6. Really impressive work Chris!! Looking over your blog it seems you've been working on this project nearly full time for over a year, how do you make these jobs pay?

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    1. Kevin,

      thanks for the first-time comment -much appreciated.

      As far as what the job pays, that's between me and the client, however I will say that the project duration has been longer than anticipated. This is due to the fact I'm building two of these complex cabinets and that has nearly doubled the work, when I had more optimistic expectations early on as to what efficiencies might be realized. Also, in the past year I've become a father and that's severely crimped shop time. Then i lost a month because i was sick.

      If I had been building a single cabinet and had not had a child or been sick, then I would have finished this piece several months back. Still, this has without doubt been the longest furniture build of my career, whether I had finished several months back or not.

      The most important thing in all of this has been to have a supportive and patient client. At certain junctures i suggested stopping work on the second cabinet and concentrating only on his piece, but he insisted I keep going on both. Clients like that are rare in this world I think.

      Whenever I worry about how long the piece is taking, i tend to reflect upon how long it will endure afterwards, and that makes a week or a month or three longer build period seem less important. At the end, I want to deliver a high quality piece and not rush anything or cut corners to meet a deadline. People, I think, get far more exercised over a bad delivery than a late one.

      ~C

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  7. Thanks for the time you take to publish Chris, I appreciate what I learn from you. Re the Oilite bearings, just noticed you might want to put a washer between the bearing and the wood if you don't have that intention already--the oil will wick out of the bronze and into the wood otherwise.

    best,
    norm

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    Replies
    1. Norm,

      thanks for the comment and sharing that information. I learned something from you in regards to Oilite bearings and wood. After some reading, it turns out that Oilite bearings can be de-oiled by soaking in an aromatic solvent for 12 hours. I'm thinking I'll do that, then evaporate all the solvent off, then seal the surfaces of the bearings which come into contact with the wood (and the surfaces of the wood in contact with the bearings as well) and re-oil the portions of the bearings with the metal-to-metal contact surfaces. More research needed yet however....

      ~C

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  8. Follow up: I had been planning to glue the bushings into the wood using silicone. With consideration of the oil wicking issue with the bearings, i think that after I've solvent treated the bearings to remove the oil, and burned any excess solvent off, I will glue the bearings into the wood using Permatex 82180 Ultra Black Maximum Oil Resistance RTV Silicone Gasket Maker, which is highly flexible and much more resistant to oil than regular silicone. That will form a barrier between bronze and wood. Then I can apply lube to the inside of the bearings where the metal-to-metal contact occurs and that should solve the problem entirely.

    ~C

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  9. Interesting Chris. Sorry, I didn't mean to complicate things for you. I wonder if given the application (very low velocity, low load, no shock--or hopefully no shock)a straight bronze bushing might be appropriate? When I encountered oilite bearings years ago, I remember being surprised to realize that the porous structure of the bearings makes them much softer and more brittle than I expected--it's sort of like bronze sponge rather than bronze. I guess it's a matter of weighing the durability benefit of self lubrication.

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    1. Norm,

      don't worry about the added complication. I'd rather be aware of possible repercussions and decide if I need to deal with it in some way. I might look to see if I can get dimensionally identical plain flanged bearings in non-lubricated bronze, though I think the Oilite will work fine for this application. Thanks for the input.

      ~C

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    2. Seems like all the commercially available bronze flanged bushings are oil impregnated. So, I'll be going the solvent and RTV silicone route. Not a big deal at all.

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  10. Really very nice work Chris! Looking over your blog is a very interesting work.I appreciated your work and really liked it. I am in the marketing department of a company who is also providing services of Joinery in Yorkshire. Honestly speaking, all my team members really like your work.
    God Bless you!

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    1. Most kind of you Rachel - thanks!

      ~C

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    2. Yoru Welcome Chris...God Bless you

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  11. Chris I must say that you are expert of your job. Great Job

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    1. Thanks very much, however i will say at times during the build process I feel anything but expert.

      ~C

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  12. They say there isn't a stupid question, so here it goes: What are you drilling those holes for? I mean, may I see the finished product, or at least a diagram, because I just don't get it. I am new to carpentry, but I am trying to learn!

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    Replies
    1. Thanks for the question Maxim. The holes are for metal pins which serve, eventually, to hinge the doors. Given that the above post is but part 87 of a process describing the build of the cabinet, I suggest taking a look in some of the preceding posts to get an idea of where things generally are in the overall process.

      ~C

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