go to page above this – “measuring etc –  tools”

for comparison with other methods go to “drilling holes at accurate distances apart”

Measuring etc – toolmaker’s buttons

toolmaker’s buttons are a set of  small tubes about 15mm od and 15mm long. They have holes in them that are  about 10mm in diameter. These tubes are are hardened and ground so that the outside diameters are all exactly the same nominal size and the ends are at right angles to the sides. One button is a bit longer than the rest.

It is not necessary for the bore to be of an accurate size or to be carefully finished.

They usually come in a set of four and are kept on a small bar made specially for the purpose. Screws and washers are used to keep them in place. But these parts are also needed when using the buttons. The bore of the buttons is significantly larger than the diameter of the screws. The washers are made so that they have a ground surface and are larger enough so that when screwed up tight they will not affect the position of the button.

fig toolmaker’s buttons

They are used for making holes at precise distances from each other.

How they are used

The workpiece, for example, a flat plate is marked out using a surface plate, height gauge, squares etc. Where there are to be holes, the center is punch as accurately as possible. This does not set the accuracy of the final holes. A hole is drilled and tapped at these points. The sizes and threads used here are to take the screws that come with the buttons.

The buttons are fitted to the workpiece loosely using the screws and washers supplied. One button is positioned as accurately as required and screwed tight. The other buttons are then position accurately relative to each other using micrometers etc and tightened.

The center of each button is now at the center of where the holes are required. The accuracy is limited by the accuracy of the micrometers used. The workpiece is mounted in a four jaw chuck. For each button, the workpiece is moved till, using a dti, the button is centered with the axis of the spindle. The button is then removed. The hole is center drilled and bored as required.

The phrase “center drilled and bored” needs some explaining. Because we have all ready drilled and tapped a hole in the workpiece and we can safely assume that this is not perfectly centered we cannot drill this out accurately. We cannot then reamed it. All that using a toolmakers button has done is to aligned the workpiece with the spindle. We will have to drill out the hole till we can at least get a boring bar into it. The boring bar is used to finish the hole either by itself or so that it can be reamed.

It would seem that this means that using toolmakers button like this is only going to work for holes that are bigger than about 6mm in diameter.

When the holes are very close to each other then one of these holes is fitted with the extra long button. This can be centered easily regardless of the shorter button close by. Then it is center drilled, drilled etc. Then it is removed and the shorter button sorted out.

This seems to suppose that the hole to be made is large enough that a large enough center drill will not be affected by a small hole drilled slightly off center will matter.

Alternatively

Where The final hole is too small to be bored and it seems that have a hole off center might compromise the drilling of a center it is possible to use a different type of button. See –

Toolmakers buttons – type 2

The thread of the screws

A set of American toolmakers button’s can be problematic in that the thread of the screws might not be ones for which the user has suitable taps available. The set shown above were made by LS Starrett.

Since the only critical part of a toolmaker’s button set is the buttons, if the threads are not convenient, it is probably worth making a new block with new bolts and washers with more convenient threads.

Use on the milling machine

This technique goes back a very long way. It would often have been used when the only machine available was a lathe and it would have been the only way to make holes accurately positioned. With a milling machine it is possible to position the work piece accurately using the leadscrews along the x and y axes. The need for tool makers buttons is gone.