Drive Bolt Scotch Mount

[asset189]

Been tinkering with a home made barn door / scotch mount and I'm quite happy with intial trials with a decent 80sec exposure of Vega, Lyra and  the Coat-hanger and not too much star trailing.

One thing Ive noticed is that there is a fair bit of play between drive bolt and its locating nut in the bottom plate. To-date Ive overcome this by applying an elastic band to add some tension but I'm looking for a more permanent fix. Any ideas ?  

[happy-kat]

I have the same issue on mine too much tolerance between the drive bolt and the captive nut. I have yet to add the rubber band approach but I had thought of adding ptfe plumbers tape to the drive bolt.

Could I see a better picture of the inside of yours and your clock guide please?

[steppenwolf]

The results speak well of the project despite the slack! My first thought was also PTFE tape but this is VERY thin and will soon wear out. I suspect that your elastic band is probably as good a solution as any because using any kind of 'thickening' of the threads solution could lead to binding whereas the constant pressure of the band should keep things flowing evenly.

[Davey-T]

You can metric fine thread rod and nuts on EBay may reduce the tolerance, as you're DIY  minded you can cut your own thread in something and stop before it becomes loose.

Dave

[asset189]

Happy-Kat   this is a photo of the innards, only an old CD with a couple of washers for added strength in centre. Ignore the figures got a bit lost there. Best results so far have been turning 45degrees every 15 secs.  Rounded nut on top of drive bolt makes for a smother rotation .

My camera is a small Sony A5000 with APS-C crop sensor so I should only be getting 12-15 secs before noticeable star-trails.  So far ive managed 80secs with this mount .

thinking about substitution the longer nut visible on bottom side of drive bolt for the standard one which might ireduce the slack a little.   Over all for something that cost less than £20 I'm more than happy.

When I get round to making version two Ill put the drive wheel on outside of top board so I can see it better .

[happy-kat]

Thank you for the image.

Similar to mine, I have an old CD as my marker and also a smooth round nut on top of my carriage bolt which glides easy on the underside of the top board as it was made from an old kitchen door unit so formica on the surfaces. I have all the bits to make it mororised with an andriono board just not got around to it.

I need to revisit my handle turning approach as I tend to do a continuous turn but can only reliably get 30 seconds using a 50mm lens thought I did manage a few reasonable 180 secs one evening. I think my images suffer from mini jolts when I turn the CD rather then the actual barn door is inaccurate. Time to try your mini eyelets with rubber bands to hold it firm.

I've put a small red LED on the underside of the top board to light the CD dial.

[asset189]

I also think that alignment plays a significant part in the quality of the end product. I've now mounted a laser pointer on the hinge which works well. Set the approx angle for Polaris using an angle meter then fine adjustment requires little more than a tweak

[happy-kat]

With my set up I don't get star trails so alignment is ok I get little wibbles which I think is where the bolt play is showing. I can't adjust the angle as I made a base wedge the whole unit sits on a chair/table top. No laser possible here I live under a flight path.