|Nigel Watts||11/10/2020 17:01:24|
|49 forum posts|
I recently acquired a Proxon 500 non-CNC milling machine and, never have had any tution and precious little experience with milling, I am slowing acclimatising myself to it by making simple pieces of tooling such as lathe tool holders, T-nuts etc (my interesting is clockmaking).
To get myself started I bought a reasonable quality machine vice (c. £70 from RDG Tools), a set of parallels, some T-nuts and other clamping devices and a mini dial indicator for set-up purposes. I have also just taken delivery of a Vertex 4" rotary table plus dividing plate set.
My first mishap was caused by the vice slipping and the end milling gouging the work. It took me a long time to work out what the problem was as I had tightened everything down very firmly. It turned out that the T-nuts were fractionally higher than the bed so the vice was not being pulled firmly down onto it even when the bolts were tight. That was fixed by filing the nuts down a touch.
My next problem was that I was getting slightly uneven depth of cut from left to right. I thought this might be swarf getting between the vice and the parallels and/or the work, which I think it partly was, but even after cleaning everything carefully there was still a small difference. I put the dial gauge in the chuck and tested the flatness of the bed in the left to right direction and did the same for the base of the vice. The bed is fine but the vice base has a difference of about 0.04mm across its 30mm width.
Is this something to worry about and if so what is the best way the correct it? Filing the underside of the vice would seem to the the proper way but that would be much harder work than skimming the base of the vice.
|Nigel Watts||11/10/2020 17:20:11|
|49 forum posts|
I think I may have answered my own question. I have just tried removing the machine vice, cleaning everything down thoroughly and then replacing it. The error has reduced from 0.04 to 0.01mm. The moral of the story: keep everything clean and test carefully.
|Martin Connelly||11/10/2020 17:24:04|
1510 forum posts
You also need a machinists hammer. Hard rubber, lead or hide for example to drive the workpiece down onto the parallels after the vice is tightened up. After the vice is tight the parallels should be clamped between the workpiece and vice bed, check by seeing if the parallels can be moved with little force from the fingers. This is an easy step to forget in the excitement of making your first parts.
|Nigel Watts||11/10/2020 18:30:35|
|49 forum posts||
Thanks for the tip. I wasn't doing this but I've seen people in YouTube videos hitting the work to get it to seat properly.
|Clive Foster||11/10/2020 18:55:02|
|2458 forum posts|
Knocking work down onto parallels can be a bit counter-intuitive.
Firstly the work moves more reliably when tight in the vice. Leaving it a touch under properly tight "so it can move" doesn't work. I think it bascally bounces back.
Secondly its the momentum of the striking head not the speed of strike that does the work. Doesn't have to be a big hammer either. 8 oz deadblow does fine for me working 12" to the foot scale on a full size mill (Bridgeport). I hold the hammer shank loosely so its not under active swing when it hits the work. Back in the day an egg shaped lump of lead held directly in the hand was considered good for this sort of job. Strike would have been more like a punch than a hammer impact. Momentum not speed again.
Edited By Clive Foster on 11/10/2020 18:55:25
|1763 forum posts|
You may also want to check the part of the vice the parallels are resting on, there may be some difference in the X and/or Y axis flatness. Good idea to check the tops of the vice jaws as well so if all is OK you can reliably use those surfaces to set up work.
|old mart||11/10/2020 19:25:10|
|2185 forum posts|
You seem to be learning the machinery perfectly well, it it always a good idea to think of ways to double check why something is not right, rather than accepting the first conclusion.
|Henry Artist||17/10/2020 22:04:50|
98 forum posts
You may like to obtain and read "Milling - A Complete Course" by Harold Hall. It is book #35 in the Workshop Practice Series.
|David Colwill||18/10/2020 08:00:36|
|670 forum posts|
Although given that your mill is quite small, a 3 inch length of 3/4 or 1 inch diameter copper bar would be suitable.
|Howard Lewis||18/10/2020 15:16:28|
|3755 forum posts|
If you are sure that your machine vice is not parallel to its base, you could strip it down (remove moving jaw etc ), and use a smallish end mill to skim the upper surface until in cleans up.
It should then be parallel to the plane of travel of cutters in the spindle, on the Z axis.
To ensure that the fixed jaw is parallel to the plane of travel of the cutter in the X axis, I made up a "goal post" arrangement to which the vice can clamp, before final tightening to the table of the mill.
The goal post is lightly skimmed so that the surface to which the vice clamps is that of the cutter.
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