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UNIQUE PRODUCTS


www.awrtech.co.uk
AWR's UNIQUE TOOLS for Astronomers

The more expensive items:
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RONCHI GRATINGS
 Anyone who has ground and polished his own mirror will know that a RONCHI TEST is an extremely useful method of checking the surface accuracy on the mirror. It is a coarse grating of parallel lines about 100 lines per inch. Now, for the first time in the UK there is an easily available source of high quality gratings. These are produced by AWR TECHNOLOGY as original photoplots onto lithographic film and mounted in 35mm slides. being computer generated with precision equipment they are extremely accurate and every one is guaranteed to be original.

Another invaluable use of the RONCHI TEST is to perform a star test at night with any telescope. It is much easier to perform than a Foucault Knife Edge Test and gives just as good a result. Perfect optics will show up as parallel shadows with no waviness. If you are about to purchase a telescope then applying this test will show up any defects. The interpretation of the shadow patterns is an essential part of assessing the quality and many examples are given in the instruction sheet.

Two versions are available: 80 lines per inch and 120 lines per inch. Both come complete with instructions. The 80 is marginally easier to use. They are £9.50 each, post included.

METEOR SHUTTER DRIVE
MOTOR AND ELECTRONICS TO DRIVE LARGE PADDLE

Three special Meteor Camera Shutters have been supplied to the BAA for use in meteor triangulation, height and velocity determination. This device chops the light going to a camera so that a meteor, if recorded, will show up as a sequence of dashes on the film. Knowing the chop speed you can work out the angular speed.

Special circuits have been designed and built by AWR Technology to make a large shutter or paddle made out of balsa wood rotate at over 10 revolutions per second. Small but powerful stepper motors were used. When the load was calculated it was found that the inertial torque presented was large and the shutter would need to be accelerated up to working speed. Also the final speed had to be frequency locked to a crystal in order to achieve the required accuracy in the meteor determinations. The shutter is directly connected to the motor shaft.

Normal stepper motor drive circuits based around the SAA1027 have a problem in that the mechanical torque available drops off with frequency. However AWR use a bi-level drive circuit meaning that the motor can be worked up to much higher frequencies and maintain the torque. The meteor camera shutter application actually requires more torque at higher speeds as there is air resistance. If you calculate the tip speed it is about 40 miles per hour!

The final specification for the units are as follows:

  Lock frequency		500Hz +/- 0.01%
  Chopping period with 2 vanes	48.0ms
  Design acceleration time	15 seconds
  Motor shaft diameter		4 mm
  Motor type			ID35-114, 48 steps per rev, 6.5Ncm torque
  Power requirement		0.6A 12.0V DC
  Inertial load presented	Balsa wood 0.45m x 0.10m x 5mm

There is excess power to cope with operation in a stiff breeze. The maximum output frequency before stalling was 560Hz with a supply of 12.0V DC. The minimum time to reach lock speed was 4 seconds. (PRICE)

PTFE - LOW FRICTION MATERIAL

Also known by the trade names TEFLON and FLUON this is a remarkable material noted for its chemical inertness and heat resistance. The full name is polytetrafluoroethylene (PTFE). It has very low friction and can be used as low friction blocks in Dobsonian telescopes etc. N.B. It is very difficult to get glue to stick to it, but it can be screwed.
We do not have an easily available source for etched PTFE. 
Max working temperature . . 250 deg C
Density . . . . . . . . . . 2.2g/cm3 
Not attacked by UV, strong acids or alkalis
We sell PTFE cut from stock sheet by the square inch.
1.0mm thick . . . 25p per square inch
1.6mm thick . . . 25p per square inch
6mm thick . . . . 75p per square inch
10mm thick  . . . £1.00 per square inch

All postage paid (to the UK) but minimum order £2.00
Other thicknesses are available - please contact us.

Here are some ideas for its use:

  • 3 pads as friction blocks for Dobsonian mounts.
  • To add as a low friction bearing on mounts with rubbing plates.
  • Simple altitude bearings for Alt-Azimuth telescopes.
  • Rubbing blocks on TUFNOL in Poncet platforms.
  • Slipping clutch rubbing plates
  • Cradle rings for rotating tubes.
This material can be worked readily to shape providing you observe simple precautions. The main problem is that it slips and slides all over the place! It can be drilled, sawn, cut with a knife and planed but be careful. Make sure you clamp the material so that it cannot slip.

WARNING - Above 250 deg C fumes can evolve. If this is likely to occur, such as when the material is machined then SMOKING IS PROHIBITED. DANGEROUS decomposition products can result.

TUFNOL - ENGINEERING MATERIAL

TUFNOL is a proprietory laminated plastic based on a medium weave fabric (WHALE brand) or fine weave fabric (CARP brand), light weight but extremely strong. It can be machined easily and is widely used for bearings, gear wheels and pulleys. It is stable and can be used for surfaces which rubbing blocks would travel over, eg in Dobsonian telescopes, Poncet mountings etc.
Max working temperature . . 120 deg C
Density . . . . . . . . . . 1.36g/cm3

We can obtain TUFNOL in sheet and rod forms of various thicknesses. It is not that expensive and costs a lot less than PTFE.
We have 1mm, 2mm, 4mm, 10mm and 15mm thicknesses in stock.

Contact us with your requirments for a quote.

An alternative material for rubbing against PTFE is the brand name 'FORMICA' used on kitchen work surfaces. It is available in thin sheet from wood merchants. It can be glued onto mating surfaces.

Ring 01304 365918 to order