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Harold Hall

Workshop Processes

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Do remember to allow for the diameter of the cutter being used when setting the mill to the required radius. Traverse the table by the calculated value plus half the cutter diameter for the outer curve and the other calculated value minus half the cutter diameter for the inner curve. Do make sure that you use the correct values for each side of the tooth. Do not forget that the inside of the tooth is machined with the largest radius

 

Use only the fence to make adjustments to the position of the groove within the jaw remembering that the milling machine table's traverse is only used to set the radius machined.

 

Machining the side groves

The groves in the side of the jaws must be a close fit on the rails on which they are to move. If typically the groove measures 6mm then using a 6mm end mill may seem the obvious choice, but should the cutter be running a little off centre then the result may be oversize. However, in many cases, the load on the cutter will constrain it to run true and cut size, it is therefore worth trying on a test piece first, Even so, do only run the cutter through again as it will increase the width if it is passed through the groove a second time. If this approach is not possible then it will be necessary to cut the groove in two stages with a smaller cutter.

 

First, set up the vice on the table such that its fixed jaw is perfectly in line with the table's cross traverse. This is vital so using a dial test indicator to test this requirement is essential. With the vice positioned fix the first jaw in this with its teeth against the fixed jaw.

 

Now machine one side of the jaw and to the depth required setting the position such that the lower side of the groove is the correct distance from the base of the jaw. With that done, remove the jaw, turn over and machine the other side similarly. This will ensure that the two groves are exactly opposite, any error though in the setting of the vice relative to the tables traverse and they will end up with an X formation. Repeat for jaws 2 and 3. If you are machining the groove in two stages, machine all the grooves first at the cutter's width then return them a second time to increase the width.

 

Do aim for a width of groove that is a little on the tight side requiring a little hand fitting. Remember, it is relatively easy to remove a little and almost impossible to add some metal.