· Get a Cloudy Nights T-Shirt · Submit a Review / Article Click here if you are having trouble logging into the forums Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User You are not logged in. [Login] Entrance · Main Index · Search · New user · Who's Online FAQ · Calendar Equipment Discussions >> ATM, Optics and DIY Forum Previous   Index   Next   Threaded   Pages: 1 psi_chemie sage Reged: 05/01/11 Loc: Leawood, KS, USA need help machining focuser       #5606254 - 01/05/13 10:22 AM Edit   Reply   Quote Quick Reply   Any astro-machinists out there that can point me towards a focuser project for a Newtonian scope? Step by Step? I want to go real simple for this first one. I was thinking a helical focuser or a Crayford-style and only 1.25" format. I have a lathe and milling machine. For the helical it seems that all you need is to internal thread a 1.5+" ID shaft and external thread a 1.5" OD barrel bored open to 1.25" with a set screw? But the Crayford looks straightfoward as well, no gears needed..? Post Extras:       dpwoos Pooh-Bah Reged: 10/18/06 Re: need help machining focuser [Re: psi_chemie]       #5606275 - 01/05/13 10:31 AM Edit   Reply   Quote Quick Reply   The main problems with a helical is that the "speed" if fixed by the thread pitch, and they wobble. I am sure the wobble is correctable with some sort of tensioned/split-nut arrangement. The challenge with a Crayford is to get the flat on the drawtube parallel to the bearing surfaces. With a milling machine you should have no problem doing this, as folks have achieved good results with careful use of a file. Use good bearings. Post Extras:       John Jarosz Astro Gearhead Reged: 04/25/04 Loc: Chicago area, IL Re: need help machining focuser [Re: dpwoos]       #5606292 - 01/05/13 10:41 AM Edit   Reply   Quote Quick Reply   I wrote a CN article on this subject quite a while ago. You can find it here Single pitch threaded helical focusers are maddenly slow. So I turned to multiple pitch threads using old camera lenses for the source of the threads. Saves some time and results in smooth operating helical focusers. John Post Extras:       psi_chemie sage Reged: 05/01/11 Loc: Leawood, KS, USA Re: need help machining focuser [Re: John Jarosz]       #5606306 - 01/05/13 10:48 AM Edit   Reply   Quote Quick Reply   THANK you John. Once I find some plans and begin on a design I place to post pictures of the process. Post Extras:       Norm Meyer member Reged: 02/08/09 Loc: Warren, ME 04864 Re: need help machining focuser [Re: psi_chemie]       #5606570 - 01/05/13 12:59 PM Attachment (19 downloads) Edit   Reply   Quote Quick Reply   I made a helical focuser some years ago and I like it. Mine is both slow (when I want to focus) and fast when I put in another eyepiece. I used 10 tpi lead with an acme thread form. Then on the side of the housing I put a deten, a spring loaded ball bearing. I did not thread the inside of the housing only the barrel holding the eyepiece. just pull on the barrel and it comes out as much as you wish or push in and the barrel goes in. Each time the ball pushes back on the spring and skips over the thread when you stop the ball again engages the thread and a turning motion screws the barrel in or out. You can see the small barrel on the side which houses the ball and spring held in by the set screw. Norm Post Extras:       Norm Meyer member Reged: 02/08/09 Loc: Warren, ME 04864 Re: need help machining focuser [Re: Norm Meyer]       #5606577 - 01/05/13 01:01 PM Attachment (18 downloads) Edit   Reply   Quote Quick Reply   here is another view with the threaded barrel extended. Post Extras:       dpwoos Pooh-Bah Reged: 10/18/06 Re: need help machining focuser [Re: Norm Meyer]       #5606594 - 01/05/13 01:07 PM Edit   Reply   Quote Quick Reply   Nice! How does it work in the cold? Post Extras:       Al8236 Pooh-Bah Reged: 08/18/10 Loc: 48.9173N 122.1390W Re: need help machining focuser [Re: Norm Meyer]       #5606603 - 01/05/13 01:11 PM Edit   Reply   Quote Quick Reply   Crayfordjon has posted a few different designs, here is one http://www.cloudynights.com/ubbthreads/showflat.php?Cat=0&Board=atm&N... There are others if you want to search. Post Extras:       Norm Meyer member Reged: 02/08/09 Loc: Warren, ME 04864 Re: need help machining focuser [Re: Norm Meyer]       #5606626 - 01/05/13 01:24 PM Attachment (12 downloads) Edit   Reply   Quote Quick Reply   The small barrel or rod that holds the ball and spring is made from a piece of aluminum rod 1/2" in diam. I drilled a hole into the rod about the same size as the ball but didn't go completely through,just enough so the ball was held back by the edge of the hole that remained. You can see the ball detent showing in this picture. Post Extras:       Norm Meyer member Reged: 02/08/09 Loc: Warren, ME 04864 Re: need help machining focuser [Re: Norm Meyer]       #5606646 - 01/05/13 01:38 PM Edit   Reply   Quote Quick Reply   dpwoos, I works fine in he cold because it's 99% aluminum so all the pieces shrink together (except for the ball and spring of course) you can make the hole,in the rod, with enough clearance so the ball won't seize in the hole when the aluminum shrinks in the cold. I made that mistake on a gem that I made. I like things to fit so there is no slop. The mount had CRES shafts that went into aluminun flanges.Beautiful fit at 72 deg but at 25 deg I couldn't get the mount apart to bring it back into the house when I was done observing. I've since rectified that. Norm Post Extras:       m. allan noah professor emeritus Reged: 08/14/09 Loc: Virginia, USA Re: need help machining focuser [Re: Norm Meyer]       #5606731 - 01/05/13 02:30 PM Edit   Reply   Quote Quick Reply   I built one along the lines of John's idea, using camera lens parts. I took apart about a dozen lenses, and found one that had a large ID, which i bored out to 2". Then i used some epoxy to attach an F-stop ring from a different lens to use as a hand grip for focusing. Then I glue the whole thing into a thin outer shell from a third lens. Very minimal machining in the end. allan Post Extras:       Pinbout Post Laureate Reged: 02/22/10 Loc: Montclair Re: need help machining focuser [Re: psi_chemie]       #5606791 - 01/05/13 03:06 PM Attachment (16 downloads) Edit   Reply   Quote Quick Reply   you can make a kineoptic type helical focuser without using threads and you'd be able to push/pull as well as turn the tube. also you could buy the eyepiece tube from jmi and build around it. here's a quick sketch but I would reduce the bearings from this initial concept, which is a knock off from crayford john's first focuser? Post Extras:       psi_chemie sage Reged: 05/01/11 Loc: Leawood, KS, USA Re: need help machining focuser [Re: Pinbout]       #5607146 - 01/05/13 06:49 PM Edit   Reply   Quote Quick Reply   OMG this is awesome, thank you all! I have some information to process, and perhaps a cutting tool to grind or two, but I will hopefully be able to show some progress soon! I have some ball nuts to repack. Post Extras:       scopemankit sage Reged: 01/27/09 Loc: south africa Re: need help machining focuser [Re: psi_chemie]       #5624646 - 01/15/13 03:29 PM Attachment (9 downloads) Edit   Reply   Quote Quick Reply   I have made a few crayfords, here is a rough plan and a pic. hope it helps. (Three of them are crayford helical focusers). Post Extras:       don clement Vendor (Clement Focuser) Reged: 02/02/11 Loc: Running Springs, California Re: need help machining focuser [Re: Norm Meyer]       #5625074 - 01/15/13 07:51 PM Edit   Reply   Quote Quick Reply   A method I have used with a standard UN thread form for fast focusing that would work on thin walled tubing is the multiple-start thread. For example I machined a double start 11 tpi thread using a 20UN full topping insert (thread profile height of 0.0307”) on my manual lathe that has an imperial leadscrew. The trick was to use the odd and even markings on the thread chasing dial. Even numbers (2,4) of the thread chasing dial for the first thread start and odd numbers (1,3) for the second start. Here is a picture of a double-start 5/16-11UN tap I made using this method from oil hardened drill rod. The reason I chose 11 tpi for the double-start application was that 11tpi is prime not some multiple of the lathe imperial 8tpi leadscrew. If I would have chosen 10tpi or 12tpi then the odd-even thread chaser dial method wouldn’t have worked. Also if I chosen metric pitch then I couldn’t use the half-nut lever. Edited by don clement (01/15/13 11:33 PM) Post Extras:       psi_chemie sage Reged: 05/01/11 Loc: Leawood, KS, USA Re: need help machining focuser [Re: don clement]       #5625392 - 01/15/13 10:55 PM Edit   Reply   Quote Quick Reply   Cool Don- I love your work. I want to try many methods but I have been thinking about trying a double start on my lathe- I've been playing with the thread dial and think I can do this.. I also want to try and make a tool for something like Norm's helical I love the threads. Scopeman, thank you for your contribution. That is awesome and inspiring, I can't wait to post some update. I'm moving my shop at this time, gonna be complicated .. Post Extras:       Pinbout Post Laureate Reged: 02/22/10 Loc: Montclair Re: need help machining focuser [Re: psi_chemie]       #5628642 - 01/17/13 06:36 PM Edit   Reply   Quote Quick Reply   don't know if you ever used sketchup but... here's a 3d model you can move around pull dims... 2in crayford focuser Post Extras:       Pages: 1 Previous   Index   Next   Threaded   Extra information 13 registered and 37 anonymous users are browsing this forum. 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