Author Topic: Magnetic Tape Encoders  (Read 1881 times)

Offline Jonny

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Magnetic Tape Encoders
« on: January 08, 2011, 09:52:07 PM »
Since this is a new thing they have not long been out and man would not have heard or seen them.
http://www.machine-dro.co.uk/index.php?target=categories&category_id=60

Heres a piccy installed on cross slide.

When tail stock butts up to two part cover i have only lost 2mm. Even the micro glass scales its a damn site larger than that and could be the prayer to most. These need to be positioned accurately within 2 degrees runout and within 0.54mm away from two part cover or they wont read!

I do have a cover that goes over the top. Thats 0.1mm between encoder and two part cover perfectly centred no shims, total runout 1/2 thou on cover, they arent that accurate an extrusion, more than good enough.
I did slap machine in a recess in carriage to lower the cover 5mm, i still needed the 90 degree dovetail in cross slide.

Thats a regular 720mm long glass scale for X axis with both cross slide i needed to beef up the protection as swarf build up will continuously be pushing on them. I dont want to keep stopping every few minutes and grabbing arm fulls at a time for sveral hours on end. More production orientated.
I need to still make something to protect over hanging two part cover but will be doubling this up with a capstan style depth stops- if i can.



Offline kwackers

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Re: Magnetic Tape Encoders
« Reply #1 on: January 12, 2011, 07:27:54 AM »
I've used exactly the same thing to my Myford 254. Glass scales simply lost me too much tailstock movement.

I'm curious as to whether the magnetic material has a life, magnets tend to lose their power over time so I wonder if the same is true of the tape.
The only other issues I've seen are: small particles of swarf can 'stick' to the extrusion (due to the magnetism) so a wiper is a good idea and you need to keep the magnetic base from DTI's etc an inch or two away from the read head.

I'm considering removing the glass scale from the rear of my milling table and replacing it with one of these to give me my original travel back - looking at my milling table I think I could fairly easily fit the whole thing inside the table castings!

(I notice the thread on fitting a readout to a lathe tailstock also uses the same magnetic strip/sensor system too)

Offline Jonny

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Re: Magnetic Tape Encoders
« Reply #2 on: January 13, 2011, 10:28:21 AM »
Likewise, i was beginning to think it was only me that had seen these magnetic type of readers.

On this particular machine an M300 i could have used the conventional glass B or C type covers after where the cross slide finishes - plenty of room before getting near the splash tray about 2 foot.
As you quite rightly mention if you require 100mm movement you would buy 1 increment of magnetic strip, it will come 160 to 170mm long. The smallest length of cover cut to size as little as 152mm. With the glass you are stuck with next available size up plus the extra length for reader plus extra for oerhanging covers etc.

I placed two orders for the encoders at separate times, you will notice one blue and one black in the tail stock venture. Turns out the magnetic strip is to suit the specific encoder but have now standardised on the black.
Must say the aftersales sevice from Allendale was superb, knowing everything inside out.
Now swapped around read and measure perfectly, not ideal and risky had to convert one already drilled through fixing points 4.1mm from tail stock to M5 not knowing what would happen and drill through the other off cross slide M4 to 4.1mm through.

Was thinking about a similar application on bigger mill. I have had a glass jobby on there for 4 years, no way out needed access to T slots etc on front to clear two lots of carriage stops, power feed and still get under the dividing plates= impossible.
With these magnetic encoders the slimness and substantially reduced reader i can get one on but would cost over 200 compared to glass at 132.