DIY - OAG

[fwm891]

Gina, Look carefully there are differences between the Warco Super Mini and the Chester Conquest Super (even though they look v similar). The Warco has hardened bedways and a meatier tailstock. The Chester states that it has a set of change wheels for either metric or Imperial threads the Warco only states what threads the machine will do, but doesn't say how. I can't imagine a lathe of that price has a gear box so I would think it has like the Chester a set of change wheels. If it has a gear box go for it. Checking charts and changing change-wheels is a pain.

Look at the accessories as well - bit like printers, the machine is cheap its the add-ons that spiral the cost.

[Gina]

I'll have to draw up a list I see the Warco has a more powerful motor That's greatly in it's favour I think - nothing worse than an underpowered power tool!

[Gina]

Regarding OAGs, I see you're using a 10mm prism whereas mine has a 6mm prism - would this make a big difference? I rather like the idea of making my own. Clearly tilting the prism is helpful and a mini Crayford focuser would be very nice. Are you using PTFE to lubricate the slide?

[fwm891]

Gina - I think the SX OAG has a 10x8 mm prism which I would say is better than my 10x10. The extra size helps to fill the guide camera CCD with light right across the frame - giving brighter and more guide stars. That aperture needs to extend right up to the chip or you will get shading. The tilt/rotate is good but once set you probably won't move again unless you plan to change between scopes of different focal ratios (not focal lengths as its the ratio that sets the angle of the light rays into the prism).

The little crayford is a great addition but if you have a lock then focus will remain fairly constant - minor differences for refocus with different make/colour filters.

PTFE is the medium I've used between the tubes.

[Gina]

I've got an image of a distant tree on my QHY5 with the OAG now by moving the main focus on the scope further in from main camera focus and the guide focus is right in. (I cured the orientation problem I nentioned above with a delrin spacer and now have the guide cam well clear of the FW.) This means that there is no way I can get focus on both main camera and guide camera at the same time - the guide camera needs to go further in than it can. No wonder I couldn't get it to work before

Sorry to hi-jack your thread Francis - guess I should start one of my own.

[JamesF]

I have the Conquest Super, Gina. It's one of a whole bunch that appear to be made by the same Chinese company with minor differences for each vendor. Warco, Axminster Tools, Chester Machine Tools and ARC Eurotrade (definitely worth a look) all seem to sell what is basically the same model and there's one that's often on ebay which is basically the same thing too. I think they're often all referred to as C3 models. Personally I'd really not want to go a lot smaller. Since getting mine I have actually thought once or twice that I should have got something bigger, but I shall hang on to it whilst I'm learning my way around. Perhaps the most irritating thing about it is the lack of a quick-release mechanism on the tailstock. The smaller lathes don't seem to come with them, though I think it's possible to buy a replacement tailstock that has one.

I wouldn't bother with the versions with DROs on the cross slide and top slide that some people sell. Mine has them (it came that way and I was buying second hand) and in the cold and damp of my workshop they're a bit unreliable, although they work fine if I take them off and bring them into the house for a while to warm up and dry out. If it were practical I'd probably remove them.

Unfortunately like astronomy the initial purchase cost is not the full story. You soon find you want more tools (though if you're up for grinding your own then HSS blanks aren't that expensive), some decent measuring kit (good vernier calipers or micrometer), indicator gauge(s) and stand(s), morse taper drill chuck, centre drill bits, probably a four jaw independent chuck, maybe a fixed steady, a saddle stop and so on. I think it's well worth considering second hand for that reason.

If you're over this way you're more than welcome to come and have a look at mine to see what it's like in the flesh.

James

[JamesF]

Looking at the pictures earlier in the thread I think you might find you need a vertical slide and some milling tools, too. There is a vertical slide for C3 size lathes. Not sure about the smaller models.

James

[Gina]

Thank you James - very interesting I won't rush it and have a good think and research as much as I can. Probably be next month at the earliest unless a cheap 2nd hand one crops up, need to gather the funds

[JamesF]

They do come up on ebay every so often though you may need to travel a bit. I was fortunate with mine in that I saw one in Helston and decided that I couldn't justify travelling that far despite the auction finishing at a price I'd have been prepared to pay. Then a few weeks later the same lathe came up for sale in Taunton. Turns out the chap that bought it in the first auction only wanted it for machining some parts that he couldn't do with his existing (much larger) lathe and always planned to sell it on afterwards.

If you're not familiar with them, the C3 lathes are considerably smaller than you might imagine from the photos, so transport isn't a major issue. Mine is easily less than a metre long and light enough that I can carry it by myself without needing to remove any of the tailstock, saddle or chuck.

James

[jimao22]

These days I finally finished the OAG build starting on Francis' idea. Mine is look like this. I found that making a small focuser is too tricky for me and not very usefull, the focus for guiding is not a critical factor, is even better to have a small out of focus star. So, I will make the focus by hand and than fix the camera on position with 2 screws 90 degrees one to another.

I need to paint black everything and than make some tests.

Thank you Francis.

The weight is for whole set-up - filter wheel with filters inside, both cameras and the OAG.

I will make a measurement for the finder-guider I have now with both cameras and filter wheel to see the difference. Anyway, I have some flexure right now and this nis the main reason why I need an OAG.