Another lathe leveling question

[Clunker1]

That aluminum disc can't be cheap. How thick is that? I was looking at getting a plate around 1/4 thick and use counter sink bolts to mount it to a surface plate to get by cheaper. What do you think?

 

[rwdenney]

That aluminum disc can't be cheap. How thick is that? I was looking at getting a plate around 1/4 thick and use counter sink bolts to mount it to a surface plate to get by cheaper. What do you think?

Actually, I paid a bit less than fifty bucks for it on ebay--11/5" by (in the ad) 1.25", but it was closer to 1.5" thick. The sawcuts were not straight so by the time I got it flat on both sides it was about 1.315" thick.

It's now the altitude bearing on one side of a Dobsonian-mount for an 8" Newtonian reflector telescope.

The 8" disk I used for the other bearing was $35.

I'm glad I found them on ebay--alternatives would have been pretty challenging. These would have been about four times as much from McMaster, but maybe wouldn't have required as much machining. My best ebay alternative was probably flat aluminum plate of 3/4" thickness (not as thick as I wanted, but thick enough for your testing), cut into squares and trapanned (probably) into disks on the lathe. That wouldn't have been any cheaper, but it would have been quite a bit more of a pain.

There's another guy on ebay that sells 8x8 square steel plates, 1.5" thick, to use as targets or some such. I bought one and made it into a base for an X-Y table, which required (and got) a pretty good flat surface. For both, I used my Skinner 10" four-jaw chuck, but the chuck could barely handle the 11.5" disk.

Rick "cheaper than any precision test bar one can trust" Denney

 

[verbotenwhisky]

Again, joe pie is talking about an integral head stock lathe. Things get more complicated when you have head stock alignment to deal with as well as twist. If you go chasing what you think is twist and the issue is also headstock alignment, you can be chasing your tail.

If absolute leveling is not where its at, why use a more accurate level.

I was hoping someone had experience dealing with sag, twist, AND head stock alignment.

I actually leveled mine to the world and itself as that provided a good reference, place the bubble in the center. It is true that level is level to itself though. I had to use 150 pounds of lead in one corner of the lower cabinet since, I am not bolted to the foundation, to get the twist out. I had to adjust my head stock ever so slightly but I first leveled the bed, you cannot and do not want to fight the bed and the head stock at once and it took me a couple of months to get the twist out of the bed.... I suggest taking your time and being patient, you can do a lot without fine tuning it but, for me, there was/is a great deal of satisfaction in the tunning...

 

[David2011]

Using the boss on a face plate method, runout in the faceplate wouldn't matter because the same point is being measured each time; it's just being relocated. The same method is used to square a table saw top to the blade and saw blades aren't nearly as flat as the expectations for a lathe. The dial indicator is placed on the same spot on the blade after is is rotated from toward the front of the saw and then toward the back.

It's now the altitude bearing on one side of a Dobsonian-mount for an 8" Newtonian reflector telescope.

I've spent more time over the years on telescope building sites than I have on this one so far. Those are the most awesome altitude bearings I've ever seen and they solve a lot of problems that plywood bearings have. I'll keep that in mind. I have an old Cave Astrola on an equatorial mount that I've wanted to make into a Dob for years.

 

[rwdenney]

Using the boss on a face plate method, runout in the faceplate wouldn't matter because the same point is being measured each time; it's just being relocated. The same method is used to square a table saw top to the blade and saw blades aren't nearly as flat as the expectations for a lathe. The dial indicator is placed on the same spot on the blade after is is rotated from toward the front of the saw and then toward the back.

I've spent more time over the years on telescope building sites than I have on this one so far. Those are the most awesome altitude bearings I've ever seen and they solve a lot of problems that plywood bearings have. I'll keep that in mind. I have an old Cave Astrola on an equatorial mount that I've wanted to make into a Dob for years.

But they are heavy!

I used that mount for the first time night before last. It works perfectly--time for sanding and finishing. (The old Meade 8" Newt is surprisingly good, too.)

Rick "okay, back on topic" Denney