R8 Finishing Techniques

Posted: May 20, 2011 in Resistant Materials

Initial knowledge 1

Current working knowledge 2.5

Prior to undertaking the course the most commonly used finishing technique I had in engaged with was sanding in its various guises.  Throughout the year I have had to do this process numerous times, in fact I seem to have spent a lot of time sanding and finishing at one stage or another.  This was not purely to hide mistakes! although sometimes my work has needed a little ‘tweaking’ in order to obtain a better quality aesthetic.  I needed to use glass papering for my plate rack in order to obtain smooth edges on the acrylic.  The process was started by using a  course low grit glass paper such as 80 or 120 and then moving up to the finer grit paper such as 400 where a truly smooth finish begins to be be obtained.  To get an even better finish the highest grade paper I could find was the 1200 grit and this was best used when wet.  I obtained extremely smooth edges and although quite a drawn out process I feel it is worth the extra time to get the desired effect.  To completely finish my edges I used the static buffing wheel.  Although a useful tool and well worth spending the extra 5 minutes to get a truly polished end product my piece of plastic was slightly large and awkward and so the buffing wheel is probably best used with smaller hand held items.  Such as the acrylic key ring I made in year 7 my first ever DT project!

masked off face to avoid scratching

We had a small metalwork tutorial and were introduced to filing as a finishing technique and I had to utilise this when trying to remove some excess material from my aluminium shell.  I marked the area that needed to be removed, unfortunately it turned out to be about 5mm and so I needed to use quite heavy cross filing initially.  This then progressed to a lighter cross filing using a second cut file.  The temptation is to go as quick as you can when filing although it was pointed out that long smooth strokes are much more efficient and this turned out to be the case.  To finish the edge I used the technique of draw filing with an even smoother file and I was able to turn what was a bit of an uneven jagged edge into a much safer smoother finish.  Like with most finishing techniques I found filing fairly long winded but to obtain the finish I desired it was an important process and certainly worth spending the time doing.

Different types of file:

HAND FILE: Used for general filing of metals such as steel. They are rectangular in section and are the most common type of file used in workshops.

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HALF ROUND FILE: Used for filing curved surfaces. A normal hand file with its flat cutting edges is unsuitable for filing curved surfaces. However, the half round file has a curved surface which is especially useful for filing internal curves.

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THREE SQUARE FILE: Is triangular in section and very useful when filing ‘tight’ corners / angles. The sharp edges allow the file to fit into corners when filing.

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KNIFE FILE: Knife files are very useful when filing where there is little space. Knife files are very thin and can fit into small gaps.

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SQUARE FILE: The square file is quite thin and fits into corners well. They can be used to file slots in metal or for filing where there is little space.

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Files are often graded according to the roughness / smoothness of cut. The file that has the least harsh teeth is graded as ‘very smooth’. The most abrasive of files is graded as ‘rough’. Some of the grades of cut are shown below.

http://www.technologystudent.com

Types of Metal Finishing 

Metal finishing is used to treat the exterior of a metal product by applying a thin complimentary layer to its surface.  There are numerous types of metal finishing processes that can be used for a variety of purposes. In this guide, we will review the major finishing methods, as well as applications and considerations for choosing a metal finishing process. Some of the general advantages of applying this finishing treatment to a metal product include:

  • Increased durability
  • Improved decorative appeal
  • Enhanced electrical conductivity
  • Higher electrical resistance
  • Higher chemical resistance
  • Higher tarnish resistance
  • Potential for vulcanization

Metal Plating

metal plated watchMetal plating machines use a chemical bath to coat or alter the surface of a substrate with a thin layer of metal, such as nickel or Teflon. The electroplating method generates an electric current to coat the substrate, while electroless plating employs an autocatalytic process in which the substrate catalyzes the reaction.

Metal plating provides a number of advantages as a finishing process. It can improve a product’s durability, corrosion resistance, surface friction, and exterior appearance. It is also a useful option for coating other metals. In high-volume production runs, a barrel-finishing machine is a fast and efficient plating solution. However, plating machines are generally not suited for smoothing out surface defects.

brushed metal lockBrushed Metal

Unlike plating, brushed metal finishing is an effective method for removing surface imperfections. These finishing machines create a uniform, parallel grain surface texture to smooth out a product’s exterior. An abrasive belt or wire brush is usually employed to achieve this effect. In addition, the singular direction of the belt or brush can create slightly rounded edges perpendicular to the grain.

Buff Polishing

If your project requires a smooth, non-textured finish, then a buff polishing machine may be your answer. This machine uses a cloth wheel to buff the product’s surface, resulting in a high, glossy sheen. The process is often used for decorative products that benefit from luster and smoothness.

Buff polishing machines tend to round out a product’s edges, and due to the cloth wheel’s range limits, the process is less effective for applications requiring intricate, fragile, or recessed features.

Metal Grinding

Metal GrinderGrinding machines use friction, attrition and/or compression to smooth out a metal product’s surface. There are several types of grinding machines designed to deliver different levels of finite smoothness. For example, a ball-grinding mill is an excellent fine grinder for cement products, but may not work for more extensive smoothing projects.

Most metal grinding machines consist of a substrate within a rotating drum. Rod mills are used to make metal rods, while semi-autogenous grinding (SAG) mills and autogenous grinding mills smooth copper, gold, platinum, and silver.

Metal Vibratory Finishing

Vibratory finishing machines are used to deburr products and remove sharp edges. They position material inside a drum filled with abrasive pellets and a substrate, then apply tumbling vibration to create a uniform random texture. The machine’s cycle speed and magnitude of vibration are usually variable, allowing effective treatment for a range of small- to large-sized parts.

worker sandblastingSand Blasting

Sand-blasting machines are typically employed in projects requiring a uniform matte texture. The process (also known as beadblasting) forces sand, steel shots, metal pellets or other abrasives into a substrate at high speed. This results in a smooth, clean product texture, particularly in soft metals.

Powder Coating

Powder coating applies a decorative finish that is similar to paint, but with greater durability. The process involves melting dry plastic powder onto the metal to produce a textured, matte, or glossy coating. A textured powder-coating machine is also highly effective in removing surface defects.

Hot Blackening

Hot blackening machines spread a thin layer of black oxide onto a product’s surface to create a matte black finish with high abrasion resistance. It is a high-temperature process in which the product is inserted into a series of tanks containing cleaners, caustics, and coolants. Hot blackening is most commonly used in the production of automotive parts, tools, and firearms.

Choosing a Metal Finishing Process

There are a few considerations that can help you narrow your choices in selecting a metal finishing technique suitable for your project. Some helpful things to keep in mind are:

  • Production speed: How quickly does the technique apply finish to the product?
  • Cost-effectiveness: Certain finishing machines (such as vibratory tumblers) can be expensive, but may compensate for their price by delivering faster cycle rates
  • Metal hardness: harder metals usually require more intense finishing techniques, like grinding, or may need tougher abrasives than those used on softer materials
  • Potential for vulcanization
Basic metal finishing, Von Fraunhofer, 1976
I seem to have found a friend in the orbital sander,  I found using this tool my preferred weapon of choice when faced with a large amount of sanding to do for my space saving furniture project .  Again it was a case of starting with the  more abrasive paper and working up in grades to obtain a smoother finish.  I liked using this machine as it is able to cover a larger surface area than I could have done by hand in a quicker time, but it is more suited for sheets of material and for more intricate areas you certainly have more control sanding by hand.  There have been times where I have thought  ‘I’ll just use the orbital sander’ to tidy things up but really it should only be used for getting a smooth finish not to hide any sins that may have occurred in production.  By producing substandard work it only leads to more  work in the long term so the key really is to apply quality control to every aspect of the manufacturing process to ensure that time is not wasted having to try and cover up errors.  Fortunately  it was more a case of smoothing the surface of the wood rather than spending hours trying to make my joints look like they fit as regards the space saving unit.  One instance where I nearly reached for the orbital sander was for the tops of my drawers.  After clamping and gluing them I did have one edge that was slightly raised so the temptation was there.  Instead I chose to use a plane and in particular a jack plane.  This tool was by far the best for the job and after being shown how to set up the cutting blade I was able to get a far neater even finish than I would have done by simply holding the orbital sander down in the corner of the drawer!

After a bit of arm twisting I was also let loose on the belt sander to aid with the finish of my dovetail joints, although they were neat, when clamped and pulled in they sat a little proud but the belt sander helped remove the little bit of excess and made the joints look really nice.  I understand why it is locked as I can see it being slightly erratic and it certainly travels at some speed, fortunately though I managed to keep a tight grip and not turn my work into, and I quote Joe ‘ a dogs dinner’.

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