Colin,

 

For polished mild steel bright finish – Start w 80, then 120, 160, 200, 400, 600 ,800, 1000, 1200, 1600, rubbing compound, polishing compound, jewellers rouge, then wax.

 

For hard tool steels you can go farther, with diamond polish paste C, then diamond B, then diamond A, then wax (and sunglasses). The diamond polishing is effective on hardened tool steels, but the finish will not last on mild steel if in fact you can even achieve polish so don’t bother, for 99.9% of ME work.

 

If you are going to paint the mild steel surface, there is no need to go higher than160 or 200 grit.

 

Collets are work or tool holding fixtures. They are usually cylindrical and have some sort of compliance built in (saw cuts lengthwise or rubber segments are most common) so they can squeeze the workpiece concentric to the collet centre. Usually there is a taper on the outside diameter to help the collet grip, and a thread is often used to pull the collet onto the taper and hold it to grip the work. Collets are usually hardened steel. There are many types of collet for lathes and mills, the common ones being Morse 3 taper, 5C, R-8 and ER. Usually a special chuck is used to hold them although Morse taper ones can be used directly in a matching size MT female spindle on a lathe or mill. When you buy collets you can buy a set of common sizes or individual ones. You can also buy soft ones that can be bored out to suit special jobs, called “emergency” collets. In a lathe collets are great for holding small work concentric to the spindle and they allow good tool access to small work. In mills the R-8 ones are great for holding endmills and other cutters.

 

John, re indexing – your description is very good. I would only add that the three most common indexing methods for ME’s are using a dividing head, using the collet type spin index with dividing plate, and using the bull gear teeth on a lathe to index, in combination with a stop pin or strip. To see pics of the spin index and dividing head use google or try http://www.kbctools.com.

 

JD

Remember when polishing with abrasive cloth and paper, each change of grade must be at right angles to the previous grade. What you should see is the scratches caused by the previous polishing at right angles to your efforts. When you can no longer see any scratches that is the time to change to a finer grade of cloth/paper. Again at right angles to the way you were working. Polishing round objects is a bit problematic, if you are just polishing and not concerned with maintaining a dimension then just keep the cloth on the move vigorously with the lathe running fairly slow, do not be tempted to dwell as you will polish grooves into the workpiece, you should end up with a figure of eight look to the surface. Change of cloth reverse the lathe. Do not be tempted to start with too coarse a grade of cloth, if it is not coarse enough you will soon see. When polishing do not back the cloth with a file, one slip and you will spend ages removing the file mark. A piece of wood 3/4″ wide x 5/16″ thick and 10″ long, shape the end like a cold chisel, take your cloth and tear it twice the width of your wood, double it over lengthwise and place it over the wood so that one side of the abrasive is against the wood fold the end over the wood so that you have about 2″ you can hold onto. Then start polishing with one of the chisel edges. When the cloth becomes clogged move it to a fresh place.

Hi Colin,

 

I’m not trying to dodge the issue but engineering, and by association, model engineering, is a very wide and complex discipline. To try to explain and define all the terms you might come across would fill several volumes. As a beginner I would suggest that as you come across various terms you use Google or Wikipedia as a first enquiry and if you still have problems, then post questions on the forums, and there are many on the internet.

 

As an example, you asked about colletts (sic) the actual spelling is with one ‘t’ i.e. collets. If you use Wikipedia here you will find an excellent explanation with diagrams and pictures, much better than I, or most others on this site, can provide.

 

Further, there are many, very readable , books on the subject available from book stores and libraries as well as magazines which make excellent and entertaining reading.

 

I’m afraid there is no easy substitute for research and reading on the subject. Having said that of course we will do all our best to help but as I said it is a very wide subject. So keep asking.

 

Best regards and good modelling,

 

Terry

Noticeably absent from all of the above, if you really must polish in the lathe with emery or any other abrasive, cover the slideways or you may end up polishing (wearing away) an item you would rather not change for the worse!

Sorry KWIL

Some things you just take for granted and forget to mention them. But yes covering the bed is a must when polishing in the lathe. I use a J-cloth soaked in oil so the particles stick to it.

Posted by Steve Garnett on 07/03/2011 10:44:03: