It's not much help, Rod … but I have to say that the ground ones, on the site you linked, look magnificent.

MichaelG.

I'd space the bars apart by 120 thou at one end, perhaps with some intermediate spacers, and screw them to an equally long or longer base bar of accurate section using location dowels and countersunk screws into the underside of the bars (won't affect their use).

Now make some sort of guide jig on the mill table to allow you to align the base bar centrally under a 60-degree cutter and truly parallel with the long axis of the mill table. Fitting each bar in turn you can machine them in lengths of 18" at a time, unclamping and moving the base bar along to a new section.

Done well, any step between sections should be well under a thou and could be removed by hand finishing a short section.

Neil

Hi Neil.
The main thing is your novel approach to the problem. That way of doing it had not occurred to me. I'm sure someone else will comment on the trigonometry. One thing I would add is to also have some space at the end that was in contact and have the difference in the gaps whichever value turns out to be correct. This is to avoid cutting on the tip of the cutter.

Les.

Hi Rod & Neil,
Here is a suggestion that may help in positioning the bars. Clamp a length of bar to the milling table and align it so one end is offset by 10.4 thou from the true X axis over a length of 18" (This is if my trigonometry is correct ) Clamp the pair of bars against this bar such that it position the centre line between the two bars in alignment with the X axis. This bit I have not come up with a good solution unless the space between the bars allows an electric edge finder to fit between the bars to centre them. The idea now is to mill 18" as Neil suggests. Move them along 18" again clamping them against the guide bar and move the Y axis in or out 10.4 thou (Depending on which way you have moved the bars.) I am surprised no one else has replied on the trigonometry. A third opinion would help. I did not set out to challenge Neil's calculation. I could see straight away how it would work but at first I could not see how to calculate the spacing so thinking about it resulted in me doing the calculation.

Les.

A couple more things to think about before making swarf! The accuracy that you are trying to achieve seem to be threatened by the material you choose. It is quite possible that if you use bms, then this is likely to be outside your tolerance. Also,machining two five foot lengths of steel with one 4 or 6 flute cutter is asking a lot. It may be worth considering using a side and face type cutter. It would be really disappointing to achieve your goal, but then find that as the material was not stress-relieved, it has developed distortion across the section,(5 foot is a long way!). Hope this assists your planning,

Roy

Hi Rod,

Here's another idea. If you have a spindle shaper or similar, I'm thinking you could cut a sacrificial fence to the required taper on a bench saw and feed this fence along with your cane through a shaper of the correct profile.

Ed.

I was at work today, selecting some bar stock for a particular project that I am working on. I was looking at the bars end-on and, after browsing your device last night, another option presented itself, and one that I think is worth considering as it seems quite 'do-able' . Using the 25mm square section as your operating adjustment, select some hexagonal bar, (depending on size), and secure along the top of each square bar with recessed cap- head screws every150mm. With some imagination, mounted side screws will enable you to adjust the hex bar perfectly straight with a good finish and consistent depth. Hope this option is workable.

Roy

Hello Rod,

It's me again! If you were to put .006" shim under the second cap-head screw,.012" under the second and carry on until the last screw, you would achieve the desired 1 thou per inch taper. You would be able to machine the top of the hex bar parallel to the bottom of the 1" bar with your 18" travel clamping to the machine bed. Removing the shims and re-fastening directly to the bar would make the assembly more robust. If only I liked fishing, I'd love to make one!

Best of luck,Roy

Edited By Roy M on 28/03/2014 23:58:26