Nylon sheet

I am making a mirror cell to support a telescope mirror. The cell is a triangular frame made with 1 inch x 1.5 inch rectangular aluminium tube with 1/8 inch wall thickness. In mm this is 25.4 mm x 38.1 mm, wall thickness 3.175 mm.

Inside the tubes there will be 3 spherical bearings, 10 mm ID, 20 mm OD and width of 15 mm

I am following a design from an American astronomy website. In this the spherical bearings are place in housings made of Nylon which fit in to the aluminium tube.

I worked out that I need to cut Nylon bar in 3 pieces to around 34.93 mm x 22.23 mm and length of maybe 50 mm each. So I probably need a length of nylon bar of around 200 mm to allow for mistakes cutting the bar.

Direct Plastics sell Nylon 6 sheet 40 mm thick x 250 mm x 250 mm for £57.64. I wouldn't mind getting this quantity which is more than I need in case it might come in handy in future. But I don't want to pay this much.

Does anybody know where I can get Nylon cheaper or is there a cheaper material I can use? Nylon seems to working fine for the telescope cell in the U.S.A. so a similar material would be good.

The bearings will have some quite heavy duty springs keeping them under pressure, and supporting the telescope mirror, they are for collimationg the telescope mirror, which is quite heavy.

I don't know how much it weighs but it is 508 mm in circumference and 40 mm thick glass so it is quite heavy. I can carry it but it is rather hard work!

David

It may be worth contacting this ebay seller, David

**LINK**

https://www.ebay.co.uk/itm/292859794077

Prices look reasonable

MichaelG.

I know little of telescope construction (but there are others here that do) but I don't think Nylon would be the most suitable material especially if you want to machine it to high tolerances (its hygroscopic to start with). I would thing that an Acetal like Delrin would be more stable. Cost difference is insignificant compared with what that chunk of glass must cost.

Ian P

There are lots of sellers on ebay doing Delrin or acetal round bar in most sizes. Delrin is known to be stronger than Nylon & often used for making gears.

Steve.

Kitchen cutting boards?

https://www.partwell.com/press-cutting-pads

https://www.argos.co.uk/search/cutting-boards/?

Good luck, Bear..

Did you mean circumference as that would be a diameter of about 6", still a heavy bit of glass though.

As regards the material requirements, probably the most cost effective route would be to machine the rectangular chunks you need from round bar. A 250mm length of 50mm diameter Acetal is about £10

Ian P

Anyone looked or used Vesconite before? **LINK**

Perhaps this could be looked at also. Out of interest, I have a 200mm Orion Optics Newtonian, and I ended up fan cooling the main mirror cell. It cuts cooling time down from 1 hour or so to 20 mins, so definitely worth thinking about when making your cell.

Regards

Ian

Of course I meant the diameter of the mirror is 508 mm (20 inches)!

Thanks for the information, Ebay is quite a bit cheaper. I will have a look at delrin. I am planning on adding a fan to the cell.

How easy is it to machine what I need out of round bar? I have a mini milling machine. I assumed milling a sheet would be a lot easier but maybe I am wrong? I also have an Aldi portable band saw. I only use the milling machine occasionally, but it comes in very useful sometimes.

Regards

David

Acetal is a dream to machine (with sharp tools) and you will have more chance of achieving the accuracy you mentioned (34.93mm x 22.23mm ) than you would with Nylon. A sketch of the part you want to make would help here.

Ian P