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2007年6月3日星期日

Classical Chinese Furniture--The use of ingenious joinery methods

Looking at classical Chinese furniture from the ‘Golden Age’, one will surely come across a wide range of designs utilising a broad variety of materials. There are lacquered examples as well as softwood, imperial and the hardwood types. The pieces represented here only indicate the classical styles in hardwood. The beauty of hardwood examples lies in its simplicity of form and intricate ornamentation. Simple forms coupled with predetermined design concepts led to the use of ingenious and complex joinery methods.

The intricacy of the joinery can be described as being puzzle-like. Because no dowels, nails, screws or similar fixtures are employed, the most common method of putting together furniture parts is by a system of complex mortise and tenon; sliding dovetail; pressure-pegged lapped joints, etc. With each type of joinery there are numerous combinations each suited for a particular purpose.

We should note that where the contemporary furniture maker will emphasise a joint for aesthetics, the Chinese furniture maker will do the opposite and conceal most joints. Only the wood, its texture, ornamentation and form are emphasised. With this understanding we can appreciate the furniture from a totally different perspective, that is the world of hidden joinery.


For example, the mortise and tenon joint for connecting circular members at right angles requires the tenon member to have curved shoulders that fit onto the mortised member.














A mitred mortise and tenon is standard for framework but it poses a challenge to the artisan when it becomes a three corner member mitre mortise and tenon joint. (Yoong)














Chinese classical furniture craft tour

The elegant design and structural integrity of the Ming style Chinese classical furniture cannot be made possible without the skillful hands of craftsmen. In the Ming dynasty, artisans manifested their respect for the spirit of woods by first examining the grain of woods and then by using them in a furniture piece such that the beautiful grains were best pronounced.

The following is a brief introduction to how we make Chinese classic furniture. It includes an awesome 15 discrete processes - and the finishing processes will be repeated for at least four to six times, the steps could be even more. The repeated application of patch, lacquer and stain onto the furniture coupled with fine polishing allows a highly protective finish be made, yet one refined with wood grains clearly visible under a liquid luster finish.

Wood Sourcing

Most of our furniture is made with blackwood sourced from Myanmar (formerly known as Burma). The wood logs are transported to the lumber yards in China by trucks. The logs range from 2 to 4 meters in length. We then purchase the wood in units of cubic meters. Being circular in nature, the logs volume is calculated based on the areas of the two ends and the length of the log. Due to its higher quality and scarcity, each cubic meter of blackwood can be as high as 4 times more expensive than soft wood like elm. There are different types of blackwood, namely "black", "pale", and "red". We choose "pale" blackwood for our furniture as it has the finest and most beautiful grain, together with a relatively higher diameter.

After a specified volume of wood is purchased, the lumber yard will then slice the logs in different thickness according to our requirements for various furniture members, such as 1.5cm, 2cm, and 4.5cm. The logs might also be transported to dedicated saw mills for the slicing. The sliced wood is shown stacked up in upper right photo.

The burl wood we use comes from wall panels of antique houses or cabinets, which date back to around one hundred years ago. There is also new burl wood in the market. However, the wood grain won't have the gentle bud formations as the olden ones. The photo on the left shows the original burl wood panel, which doesn’t show the pattern of burl wood. However, the grain will be shown beautifully after the restoration through no less than six times of sanding and polishing. Due to its high demand and drying.

Wood Treating

Wood as a plant contains water in its structure. It is therefore very important that excess water be removed before we start using the wood to make furniture. The easy crack of lower quality furniture - in particular those made from soft wood - is due very often to insufficient drying of wood. After the wood planks are transported to the factory, they will be stacked up in a highly ventilated area for air drying. This will take from weeks to months, depending on the relative dryness of the timber. After that we use a traditional method called barn drying to dry the wood. Traditional style of coal burners are used to gently dry the wood in a tightly locked barn for one to one and a half months, allowing ample time for the wood to contract before we actually work on the wood. However, please note that the water removal process will never complete. As dry as the wood is treated, the moment it is taken out of the dry room it will start taking in moisture. Therefore in an extremely dry environment some minor contraction of wood in a finished piece of furniture should be expected. Solid wood furniture, except that literally sealed with heavy lacquer and chemicals, regardless of their age is expanding and shrinking all the time, subject to the location’s existing climatic condition. It should be viewed as a natural growth process of wood.

Members Cutting

Upon receiving a high level design diagram, the craftsmen will determine what are the best ways to do the underlying construction, and the individual joinery mechanisms. A life size template - as shown on the right - will be made on thin plywood to further cross check the design, as well as to help cut the individual wooden members. The wood planks will be sawn into individual wooden members using power saws. The sawn wooden members will then be placed into the drying barn for further drying.

Wood Pressing

The wood members are then put through a pressing machine to make them straight and flat. Before pressing, the surface of wood members shows lines of grooves created by the slicing saw in the saw mill, as shown in the top left photo. These grooves are removed by the pressing machine, during which lots of wood particles are generated. To further remove the rough fiber of the wood, wood members are then put through a power sander as shown on the right. The vigorous sanding produces abundant wood flecks. This is the first time that the wood surface is sanded.
The sanded wood members are then piled up together in a ventilated and shaded area, waiting for joints to be made.

Joinery Making

What makes Classic Chinese furniture sturdy but simple in architecture is the intelligent use of joinery. The strict rule of practice is – on Classic Chinese furniture, no nails or screws are to be used between any wooden components.

After the wood blocks are smoothed, it is now ready to create joineries. The top left photo shows a drill fitted with a mortise creation bit being pressed onto a wood member, while the lower one shows the opening of a groove.

Shown on the bottom left is a large lattice screen usually used for inlays or as window frames. The triangular pattern is formed by numerous small wood members joined together as shown in the bottom right photo. Not only does this architecture prevents the use of nails, the members can be taken out and reassembled when needed. More importantly, this method was invented hundreds of years ago as a sparing use of the precious hardwood.

The normal diameter of a blackwood tree is around 30 - 50cm. As this width might not be sufficient for furniture with large panels like dining table top, two or more wood planks are merged together in such cases. The merging is done by the traditional Chinese joinery method – tongue and groove joint. Light beige colored organic glue is added to further strengthen the bond. However, please note that glue in Chinese furniture making always plays a secondary role.

An example of merged wood is shown in the top right photo. You can easily see the joining line. However, after subsequent staining and lacquering, only experienced eyes will be able to tell where the dividing line is on a table top!

Restoring & Carving

The Restoring and Carving process is optional depending on the design and material used on a piece.

Up until now we have been discussing how we make a piece of new furniture. However, there are times that it makes more sense to use an existing one. For example, an antique screen can be used beautifully as a coffee table top. Moreover, as discussed earlier, old burl wood serves as perfect inlay panel for cabinets.

Firstly a lacquer remover is applied, followed by scratching such that the old lacquer is completely removed. This is necessary as certain recent lattice work or panels use heavy lacquer to cover the original wood grains. The joints are then taken apart and reassembled to ensure tight connection. Optionally size of screen will be adjusted to fit the desired coffee table top.

Carving may be carried out to accentuate the design and look of certain furniture. However, Ming Style furniture never over-uses carving, as it destroys the overall simple and elegant lines.

The top right diagram shows our craftsman working on an apron for a table, followed by the carving of a leg for bamboo style shelf. Note the use of cables to fix direction of leg to prevent it from turning in the carving. Each of the bamboo knot is carved this way. Counting all the number of knots in a bamboo style shelf, one can easily imagine the amount of time and effort required.

There are numerous kinds of carving knives designed for different functions, as shown on the left. A highlight of a carved leg for bamboo chair is shown on the right. The mortise is used for connecting the seating panel.

Assembling

The independent wood members are now ready to be assembled into a piece of furniture. Our workers will firstly put the wood members together to see if there needs any fine-tuning of joinery. If so, the blocks are taken out and put through automatic sanding machines like the continuous sanding belt shown on the right. For fine tuning of other surfaces, we use other sanding tools. Please note that we usually saw the wood members initially larger than their ideal sizes. For joinery, tongues (tenons) should be larger and groove (mortises) should be smaller than their ideal sizes. This enables the possibility of fine tuning in this step. Or else, the joinery won’t be as fit as desired when all the wood members are put together.

After fine tuning of wood surfaces and joints, it is now ready to do final assemble for a piece of furniture. As in the olden days, glue is used to further strengthen the joints. We take much pride in the fact that the joints we make are so fit that all the individual pieces have to be hammered in, as shown in the upper left photo. The bottom left one shows the craftsman testing the fitting of a spandrel.

Scraping & Refining

Although strange in words, this is actually what we do to the piece of furniture in this step.

Flat and fine metal file is used to further smoothen the wood surface and remove irregularities. The metal scraper will be used to scrap or peel away the external fibers of all the wooden surfaces. It will also smoothen all the curves and lines. As seen in the top left photo, the finer grains are reviewed after the surface fibers are removed. Considered a crucial step in fine cabinet making, this step regrettably is not practiced by most furniture manufacturers now.

Then, various metal files are used to smooth out and refine different beaded edges, mouldings and grooves. It takes our craftsman one and a half days to completely finish the surfaces and lines for a folding chair.
The difference made by this scraping and refining is evident - you just need to use your fingers to feel the different corners and edges of a piece.

Sanding

This can be considered the last step before the finishes steps. One shouldn't be misled into thinking that sanding is only done in this step. In all the subsequent steps sanding is done, in progressive finer grade of sand paper. In this step 120-grit production paper is used, followed later by finer ones like 240 to 400. The sanding process is a lot more difficult than what it seems. Given the many different angled curves and lines for a piece of Chinese furniture, the craftsman needs to sand the piece fine but at the same time all the curves and lines should be preserved intact. Unskillful craftsman might easily blunt beaded edges or corners made asymmetrical. Equally worse is a piece not sanded enough. In such case the surfaces won't be smooth, in particular around the corners of joint wooden members.

Patching

Just like the sanding step the patching step as described here is just one of the many that will be done for a piece of furniture. It's described here because this particular patching is done before the piece is subject to water polishing and bleaching. Subsequent patching steps, performed after the bleaching, will be intermixed with the lacquering steps.

The patch for fine Chinese furniture does not use the same materials as that ordinarily used by modern craftsmen in interior fit-out or furniture making. The chalk power is the same, but the chalk is mixed with Natural Lacquer, an organic lacquer extracted from the sap of a tree called Lacquer Tree. The Japanese call this lacquer Urushi, which is regarded as one of the highly respected traditional art form. The Natural Lacquer is irritant to the skin of many people when it hasn't been dried, so the gloves are a must in handling it. Due to the oxidation process of Natural Lacquer, the patch after having been applied turns from the original light brown to dark brown color. Contrary to normal patch, the patch won't air dry. It will only dry when the piece of furniture is placed into the Lacquer room for drying, which is kept hot and humid - the crucial environment for Natural Lacquer to dry. It takes a few hours for it to dry completely.

Before we proceed, let us look at howthis very different patch is made on the right. The top right photo shows the original Natural Lacquer, which turns dark brown the moment it gets contact with air.

Water polishing & Bleaching

The dried piece of furniture is now ready to be cleaned, water polished and bleached such that its surfaces are clear and clean for subsequent finishes steps. A bleached piece of furniture also displays more even wood grains. We use 120-grit sandpaper block together with water to clean and polish all the surfaces for one hour, as shown on the left. The piece of furniture is then left under the sun to be dried completely. Alternatively, electric dehumidifier can be used in an overcast day. The lower left photo shows the water polished piece of furniture.

The piece of furniture will then be sanded again with a finer sandpaper (240-grit), followed by another round of patching and drying in the Lacquer room. After the piece of furniture is dried, it will be bleached.

As can be seen in the photos on the right, the yellow substance is the impurities being removed. The piece of furniture will then be cleaned with water and then dried under the sun. To completely remove the bleach, this water cleaning and drying process is repeated for six times. It won't be hard to understand the labor intensity involved.

The bottom right photo shows a chair after the bleaching and cleaning. You can see that the grain of wood is much more evident. It is also much purer and uniform such that subsequent stain is easier to be applied. This piece is then put into the dry room for complete drying before we formally proceed into the finishes step.

Staining

After the piece of furniture is dried thoroughly, which takes a few days to weeks, it is then patched, dried and sanded with finer grain sandpaper (320-grit). The particles are then blown away by pressurized air, as shown anti-clockwise from the top left photo.

We will then apply stain to the piece of furniture. The stain is a mixture of water dissolved red, yellow and green element colors. The stain is applied not with brush but with a piece of rag. The stained piece of furniture is much darker than the original one. It is now brought to the dry room for drying again. The dried piece of furniture is shown on the right.

This is just one of the several staining cycles that will be performed. To ensure the stain is absorbed deep and even, no matter how light or how dark a piece is, this step will be performed multiple times.

Lacquering

The dried piece of furniture is now ready to be lacquered. The lacquer is the same as the one mixed with patch and applied before the water polishing process. It is called Natural Lacquer, used by all the fine antique furniture in the olden days. The finish created by Natural Lacquer is unparalleled, being a lot more attractive and protective to the piece of furniture.

To dramatically cut short the time and cost in the finishes steps, lots of furniture makers nowadays will apply a thick coating of synthetic lacquer (or what is called hardener in the trade) before Natural Lacquer is applied. Though the furniture may also be claimed to be made of Natural Lacquer, it however lacks the natural beauty and understated sheen of pure Natural Lacquer. Contrary to pure Natural Lacquer, this kind of finish won't improve over time, and will give off an artificial plastic film like effect on the surface.

The Natural Lacquer is applied by a rag over the furniture surface, much like rubbing furniture oil - but a lot more strenuous. As the Natural Lacquer won't air dry, so the rubbing can create a very fine and edgeless effect without fear of partial drying during the process. The piece of furniture will then be taken to the Lacquer room to dry, which will take a few hours time for complete drying. It takes a lot of skill to maintain a constant highly humid and hot environment in the Lacquer room, especially considering the wide variety of environmental conditions.

Fine Polishing

After the lacquered piece of furniture is dried thoroughly, it will be fine polished in sequentially finer abrasive materials, from fine grade of sand paper to the ultimate finest grade of steel wool - as shown on the left. The process will sand down the lacquer to a very fine surface.

The piece will then be put into the dry room to dry again, waiting to start the finishing steps all over again - patching, staining, lacquering, polishing and then drying. It is only through this repeated steps that a fine but protective finish be made. It takes us at least five times of finishing cycles to produce our trademark finish, and for rougher wood surfaces it may take us up to eight times.

Had we opt for the synthetic finish, or the shellac finish much used for the rustic looking furniture including antique, the finishing time can be cut short to just two to three days. It may be tempting to think otherwise with the advancement in technology but the old saying is still true - it takes slow and long time to make fine pieces. There is simply no magic to beautifully crafted pieces.

Waxing

To provide further protection to the piece of furniture, and as a final dressing to the finish, wax is then applied to the whole piece of furniture. It is now ready to be quality checked and packed for shipment.



(IMix)

2007年6月1日星期五

明式家具的科学性

明式家具大多从实用角度出发,根据人们日常生活的需要确定结构和造形。在此基础上,再进行必要的修饰,达到使用功能和造形艺术的完美结合。明式家具的科学性主要体现在造型设计和榫铆结构两个方面。

一. 造形设计

明式家具在造形设计方面基本与人体各部位的结构特征相适应。如:椅凳的高度在40-50厘米之间,大体与人的小腿高度相等。大形坐具,因形体比例关系,坐面较高,但必须有脚凳配合,人坐在上面,双脚踏在脚凳上,实际使用高度(由脚凳面至坐面)仍是40-50厘米。桌案也是如此,人坐在椅凳上,桌面高度基本与人的胸部齐平,双手可以自然地平铺于桌面,或读书写字、或挥笔作画。两端桌腿之间,则留有一定空隙,桌牙也控制在一定高度,以便于人腿向里伸屈,贴近桌面。椅背大多与人的脊背高度相等,后背板根据人体脊背的弯曲特点设计成曲线形,且与坐面保持100-105度的背倾角。坐面多用藤心,由于藤屉富有弹性,在承受压力时自然下垂,形成3-5度的坐倾角,这正是人体保持放松姿态的自然角度。其他如座宽、座深、扶手的高低及长短等,都与人体各部位的比例相适合,有着严格的尺寸要求。

有关明式家具的制做,早在万历年间午荣编著的《鲁班经匠家经》(简称《鲁班经》)一书中,就有过详细的介绍,并对各种门类的家具逐一作了规定。

明式家具造型的突出特点是侧脚、收分明显。以明代黄花黎平头案为例,其正面案长200,高82厘米,两侧案腿外留出25.5厘米的案头。两腿上端内距为133厘米,下端向外撇开,足端内距142厘米,两腿各侧出4.5厘米。侧面,案宽59厘米,两腿在案面冰盘沿以里与案面结合后微向外撇,两腿外距与案面宽度相同。两腿内距上端45、下端47,各侧出1厘米。

再如花黎木小长桌,桌长92、宽49.5厘米,正面两腿上端内距60、下端内距66厘米,两腿各侧出3厘米。侧面两腿上端内距39.5、下端内距41.5厘米,两腿各侧出1厘米。其他如靠背椅、方凳、面条柜等,也都有明显的侧脚。明式家具侧角大多体现在无束腰器物上,束腰家具侧角不甚明显,有的根本无侧角。明式四件柜都无侧脚,以免并排摆设时中间出现缝隙。因此,明式家具的侧角并非普遍现象,而是专指无束腰家具而言。

二.榫铆结构

明式家具坚固耐用,除其选材质料较硬外,还在于其科学合理的榫铆结构。一件家具,往往由若干构件组合而成。构件与构件的结合处,都要通过各种形式的榫铆,将各个构件巧妙地连接起来,组成一件完整的家具。

明式家具常用的榫铆结构有以下几种:

一)横材与竖材结合的丁字形结构

横材与竖材的结合又称“格肩榫”。如:桌、椅、凳的横枨,柜身和柜门的横带与立柱的结合,均采用这种作法。格肩有大格肩、小格肩之分。大格肩又有实肩虚肩之别,小格肩则都是实肩。实肩是在横材两段作出榫头,在榫头外侧作出45度等边三角形斜肩,三角形斜肩紧贴榫头。在竖材造出榫窝,并在外侧开出与榫头上三角形斜肩相等的豁口,正好与榫头上三角形斜肩吻合。格肩的作用,一是辅助榫头承受部分压力,二是打破结构处平直呆板的气氛。虚肩也较飘肩,它与实肩的区别在于三角形斜肩不是紧贴榫头,而是在榫头之间留出空隙,不与榫头相连。在竖材的榫眼外侧,也挖出与虚肩大小、薄厚相等的豁口,但不与榫眼相连。这样做的目的是为了少剔去一些竖材,以免削弱立柱的支撑能力。在桌类、椅凳类的上下横枨上,常常采用这种作法。这是大格肩做法。小格肩是把紧贴榫头的斜肩抹去一节,只保留一小部分。这是一种比较科学的作法,它既保持了竖材的支撑能力,同时也照顾到辅助横材承重的作用,一般用在柜子的前后横带上。

还有一种作法,是横材与竖材都是圆材,为了把横材、竖材连接得圆润、柔和,使横竖材的圆面齐平,在横材榫头两边作出弧形圆口,包住竖材。丁字形结构还有格肩和不格肩之分。如果在明面上,一般都采用格肩做法,但在人们视线不易接触的部位,则往往不用格肩。不用格肩的做法,又有透榫和暗榫之别,有的家具即透榫与闷榫混合使用。如:为了加强边框的牢固性,通常将桌面四框中间穿带作一条或两条透榫,其余均作暗榫。透榫要视桌面的长短和穿带的多少而定,如果是三条穿带,只在中间一条做透榫,如果是五条,则把中带两旁的两条作成透榫。

二)直材角结合

直材角结合,即桌案、椅凳、柜门等板面四框的结合,或椅背、扶手等立柱与横木的直角结合。板面四框结合多用“格角榫”,它也有明榫与暗榫之别。明榫多用于在桌案板面四框和柜子的门框,桌案的边框一般分长边和短边,长边称“边挺”,短边称“抹头”。在边挺和抹头的两端作出45度斜边,边挺作出榫头,抹头作出榫眼,这样就把明榫处理在两侧,而正面则可以给人一个明快整洁的外观。

凡结合后不露榫头的都叫“闷榫”或“暗榫”。暗榫的形式多种多样,仅就直材角结合而言,有单闷榫和双闷榫。单闷榫是在横竖材的两头一个作榫头,一个作榫窝,双闷榫是在两个拼头处都作榫头,在紧靠榫头处又凿出榫窝,使两个榫头可以互相插入对方的榫窝。由于榫头形成横竖交叉的形式,加强了榫头的预应能力,使整件器物更加牢固。

还有一种闷榫接合方法,即横竖材都切出45度斜面,在斜面上凿出榫窝,再用一长方木块插入两边的榫窝,用胶粘牢。直材角接合也有不用45度斜面的,而是在横材下面作出榫窝,直材上端坐出榫头,将横材压在竖材上。这种作法多为圆料,俗称“挖烟袋锅”。明式靠背椅、扶手椅的椅背和扶手的转角处常用这种作法。

三) 拼板和框内装板结构

制作大型家具时用料较宽,常需用数块板相拼接。但木料软硬不同,纹理不一,往往出现翘裂或变形现象。为了使拼接处始终保持平整光洁,必须采取适当的措施处理接缝。常见的薄板拼合是在板面纵向断面起槽,另一面做出与边槽相应的榫舌,把榫舌镶入槽口,用胶粘牢。这种做法,木弓匠师们多称为“龙凤榫”。如果材料不足,数板拼合刚好够用,若再做榫舌就会使板材亏损,这时就应在两板材拼面都开槽口,然后再另做一板条镶入两边槽内,使两块板拼合在一起。
稍厚一点的板材拼合,用在桌面或案面上,多采用穿带榫。就是把板条严好缝,再横开数道底宽口窄的梯形通槽。在穿带的一面作出与槽口断面相应的榫舌,将穿带一头对准槽口向里推,使板材固定在穿带上。这样,板材四边有边框束缚,中间有穿带相连,形成平整光洁的整体。

家具的面板或柜子的顶、门、两山及背板,大多采用框内装板的作法。具体办法是在四框内侧打槽,将板心的四边镶入边槽,这样就把板心边沿处理在暗处。既增加了家具的美感,又加固了板心。镶边有两种形式,一种把板心边沿做出与边框槽口深度相同的榫舌,板心镶入通槽后,板面与边框齐平。木工术语称之为“不落堂”,凡桌案表面都用这种作法。另一种是将板心四边削成斜坡,使板沿镶入槽口。这种作法表面上不是平的,面心四周低于边框,木工术语称之为“落堂”。

四)腿与面及牙板的结合

腿与面的结合有长短榫和夹头榫两种。桌形结体家具不论有无束腰,多用长短榫;案形结体家具则多用夹头榫或托角双头榫。长短榫又分综角长短榫和柱顶长短榫,其特点是两个榫头一长一短。它的作用是把边挺和抹头固定在一起。长榫连接边挺,短榫连接抹头。之所以把一个榫头作成短头,是因为腿端竖榫与桌面横榫发生了冲突,如果不把这个榫头去短,势必顶住边挺伸向抹头的榫,使板面落不到底。

综角榫结构是在桌腿与板面边框衔接处自长短榫的根部起向上削出45度斜肩,斜肩内侧挖空,板面边框转角处靠下一点的位置亦剔成45度斜角,组合时边框斜角正好与腿上的斜肩吻合,使边框外沿平面与腿的外平面拼合成一个平面。结果只在结合处留三条棱角和三条拼缝,而这三条棱角和三条拼缝又只有一个交点。由于它具有多角形的特点,故此人们常呼之为“粽角榫”或“粽子角”。

柱顶长短榫与粽角长短榫的不同之处是榫头的外面没有斜肩,它和板面组合后,板面不是与腿的外面齐平,而是伸出腿面。这种做法使腿足的形式富于变化,圆腿、方腿均可,不受面沿限制。而粽角榫结构则不然,它只能随面沿的形式作成平面,所以粽角榫结构的腿都是方的。

案形结体家具腿与面的结合不在四角,而在长边两端缩进一些的位置上。前后两面多采用通常的牙板贯通两足,形成牙板固定腿足,腿足夹固牙板,牙板又辅助腿足支撑案面的多功能结构。这种结构,人们称为“夹头榫”。其作法是在腿的上端开出横向豁口,豁口两边做出两个与腿的宽度相等的榫头。牙板厚度要大于豁口宽度,将牙板需要插进豁口的部位按腿的宽度剔去一些,使穿插部分的厚度与腿上豁口宽度相等,这样牙板插进豁口后就不会扭动。牙板的高度一定要与榫头的底部齐平,牙板由牙条和牙头组成,讲究的用一块整板做成。再上是案面,案面的边框一般比桌面边框宽。在与腿结合的位置凿出榫窝,与腿上端的双榫头相吻合。

插肩榫,也属于夹头榫的一种形式,作法与夹头榫基本相同。它也分前榫和后榫,中间横向开出豁口,把牙板插在里面。不同的是前榫自豁口底部向上削成斜肩,作成前榫小、后榫大、前榫肩、后榫平肩的榫头。插肩榫的牙板也要剔出与斜肩大小相等的槽口。它和夹头榫牙板所不同的是槽口朝前,组合后牙板与腿面齐平,在看面上留下两条梯形斜线,在一定程度上还起着装饰作用。

抱肩榫,其结构与粽角长短榫原理相似,实际上是把粽角榫的斜肩移到榫头以下,这样斜肩交合的也就不是板面边框而是面下牙板了。因粽角榫板面斜肩与边框为一木做成,所以两个斜面只要合缝就行了。而抱肩榫的牙板和腿部斜肩必须做出榫头和榫窝,才能使牙板固定在腿上,以辅助腿足支撑案面。这类榫铆结构大多用于束腰家具。

挂榫,是一种酷似抱肩榫的结构。从外表看,它和抱肩榫的位置、形式完全一样,但内部结构却与抱肩榫有所不同。它在抱肩榫结构基础上又在榫头的两个外面的下部各做一竖向挂销。挂销的外面要比内面宽些,在牙板内侧也要做出与挂销大小形状相同的通槽。组装时,将牙板的通槽对准挂销按下去,使腿和牙板的斜肩合严。这种结构在作用上有拉有挺,可以有效地使四足及牙板牢固结合,如床榻类的大型家具多采用这种结构。凡使用这种结构,足下无须另装底枨和托泥。
霸王枨,是一种“∫”形曲枨,它不是装在明面上,而是从桌腿的内角线向上弯曲、延伸,并固定在桌面下的穿带上。这种作法多用在低束腰家具上,它既可帮助牙板固定四足,又能对桌面穿带起支撑作用。这里霸王枨与腿的结合部位通常用勾挂榫。其作法是先在霸王枨的一头作出榫头。自榫头顶部向根部削成斜坡,在腿的内角线上凿榫窝,里侧略高于外口,再做一小木塞,将榫头插进榫窝,使榫头上斜面与榫窝上斜面抵紧,下面空余部分用小木塞塞严。这样就把腿和枨牢固地连接了起来。

五)托泥与腿足的结构

托泥是装在家具足下的一种构件,作用相当于管脚枨。托泥可分为两种类型,一类是框式,包括方、长方、六角、八角和圆形、花瓣形等,具体形状要视面的形状而定;一类是垫木式,是用一长方木方装在案足之下。框形托泥多用在有束腰家具中,因为这类家具多用抱肩榫,牙板只起支撑的作用,而管束腿足不向外张的拉力却很弱。为了弥补这一不足,便采用了在足下装托泥或管脚枨的做法。这样从家具整体各部分相互配合的角度分析,腿足顶端、足端分别有桌面和托泥管束,中间的牙板只起支撑作用,仍是一个科学合理的整体。托泥的作用还在于保护家具,延长家具的使用寿命。因为一件家具陈设时间过久,接地部分难免受潮腐烂或因挪动而磨损,一旦出现这种情况,只须更换托泥即可解决。

框式托泥由边挺和抹头组成,四角结合处用格角榫连接,接缝处凿出底大口小的榫窝,在四足下端做出与榫窝相同的榫头,这种榫头大多与腿足一木做成,后来也有在足下凿眼另装的。在组装托泥四框时,把榫头对准榫窝,将抹头与边框装牢。这样在挪动时,不致使托泥脱落。进入清代,作法逐渐简单,只在托泥和足底凿眼,用一木楔连接,以胶粘合,但年长日久,胶质失效,很容易脱落。

圆形托泥多采用弧形对顶接方法,接口的多少要依腿足多少而定。如果家具是四足,托泥就由四段组成,五足则用五段组成。接口处都安在足下,有贯穿托泥和腿足的木销。托泥的形状与面的形状相一致,上下呼应。常见者有圆形、海棠形梅花形、双环形、银锭型等。还有一种托泥是装在案形家具上的,作法比较简单,只用两条横木,做出榫窝与腿足相连。

六)弧形材料的结合

弧形材料的结合常用楔钉榫,多用于圈椅的弧形椅圈。由于椅圈的弧度较大,必须用两节或两节以上的短材拼接而成。为了使接口竖实牢固,匠师们将两个圆材的一头各做出长度相等的半圆,在半圆材的顶端做出榫舌,再把两个半圆平面的后部与横切面相交的转角处开出与半圆平面齐平的横槽,然后把两材依平面对插,使上下左右都不能活动。但这时的结构还可以向相反的方向拉开,于是匠师们又在两材合缝处开一通槽,将一方形木楔钉进去。这样,接口处就既不会左右晃动,又不会向两边拉开,达到了竖实牢固的目的。

七)活榫开合结构

活榫开合结构俗称“走马销”。一些大件家具如床、榻、屏风等,在搬运时不可能整体移动,必须将其拆成零部件,在部件与部件连接处,宜采用此种结构。其作法是在一边凿眼,镶上木楔,木楔突出部分一般高约3至4厘米,自木楔一边向木楔中线削成斜坡,作成头大底小的榫头。在另一边上,凿出与榫头同样大小的榫窝,然后在榫窝的一头开出一段底宽口窄的滑口,把榫头对准大榫窝安下合实,再向窄口方向一推,窄口榫窝便紧紧地卡住榫头,使两个部件牢牢地连接在一起。如果需要拆开时,则从窄口向宽口方向一推,宽口榫窝一般做得较松,很容易摘下来。

上述走马销的特点是一面平直一面斜坡。也有两面斜坡的,原理与一面斜坡相同,只是一面斜坡对榫窝要求严格,它的直面必须与榫窝的直边相对。如床榻两边的扶手,榫头直面一般都朝外,推合的方向是从前向后,后背两边与两扶手连接的走马销则是自上向下按,直到靠背下边与坐面后边沿的直插榫吻合。这样就将后背、扶手与坐面牢固地连接在一起了。

明式家具的造形和榫铆结构种类繁多,本文所述只是其中较为常见的一小部分。由于笔者水平有限,欠妥之处还有赖于各位专家学者教正。(顺德家具网)