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3" bore will mean about 4" shaft OD, so you are looking at bearing up around the 7020 size. These get really pricey in the spindle bearing quality ratings.
Ebay 130385038669
Do you really need 3" bore?
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Been doing lots of reading on the forums lately and this thread
http://www.cnczone.com/forums/vertic...the_build.html
has really caught my eye. I have a bunch of HSR25 THK rail and I though man that could make a great lathe. I would like one that has a distance between centers of a couple feet IE 2-3 maybe 4. Most of the stuff I do won't be more then 12 inches long including whats in the chuck.
So here is the question I want a 3 inch Spindle bore. What is the minimum size you would make this lathe? Any reason to make it much bigger then the one shown in the linked thread? I don't plan on putting parts in it that weight more then 30 lbs at most. Is there a reason to keep the bore small?
is it going to mainly depend on the chuck I use? IE a 8 inch chuck with a 3 inch bore so my headstock needs to be at least 4.5 inches above the bed plus whatever the ears stick out on the chuck?
Oh yeah this is going to be doing 4140 and 4340 steel mostly. Might end up doing touch ups on hardened steel.
Just wondering. not sure if I want to build the whole headstock myself or if I am going to find a salvage one somewher. Any input would be great. Thanks all.
3" bore will mean about 4" shaft OD, so you are looking at bearing up around the 7020 size. These get really pricey in the spindle bearing quality ratings.
Ebay 130385038669
Do you really need 3" bore?
Regards,
Mark
www.wrathall.com
Hmm thought I replied, but I guess not.Originally Posted by RotarySMP
First Thank you and WOW!!!! That is crazy expensive. Geesh. Second. i want to be able to at least cut some 2.5'' stock. Really like being able to feed through the spindle. I might have to let my scrap hunting skills find me some large precision bearings and go with whatever size that I find.
Do I really need a 1/2 wall thickness. That seems pretty huge. I guess I am not planning on hogging anything. This will be an upgrade from a 9X20.
What should I use for the way base where I attach my rails? Looks like 48 long rails are going to be the ticket for the Z direction. I may a 24 inch cross slide. That way I can space the blocks out from eachother for more stability and hopefully better rigidity.
Thanks for the info. Where do I find the correct bearing for a said ID?
It's been said that a lathe is the only machine tool that can build itself. Outside of a couple of Gingery Lathes I've never seen an example. Get a headstock from a suitable organ donor and rebuild it if necessary imho.
The 7" in your link is a little gem, I've also considered a scaled up version and collected some parts. I keep waiting for a headstock casting to fall into my lap, should have taken one home in my lunch box back when I worked for a lathe manufacturer lol.
Anyone who says "It only goes together one way" has no imagination.
That is probably the minimum wall thickness you should consider for such a large bore. According to this, the stiffness of the spindle is a 4th power function of the wall thickness... CNC Cookbook: Mill Belt Drive, Pt 1 look for the section: "The Value of Spindle Wall Thickness"
As for sizing bearings, if you go to Search Bearings:Miniature/Ceramic Ball Bearing Finder you can search for bearings by size.
bob
The more I look at this the more I think a prefabbed headstock is probaly how I will go. Is there a particular one I should lean towards? And older atlas or Southbend perhaps?
Before you get into hardware sort out what you need as doubling the bed length has repercussions.
1. Determine the envelope you need - swing over bed and swing over saddle - through bore of head stock - length through head stock - distance between centers - the all up weight to be turned by the motor.
2. Requirements for feed rates and materials to be cut.
3. Traverse times when 'cutting air'
4. Turrets on the tail stock and or tool post - are these to be under CNC control?
5. Can the compound slide be dispensed with? There may be some parts that will require this and this may depend on the CAM you will be using and the control of the Z and X to mimic a compound.
6. Surface finish required
7. Accuracy of finished parts. Both in terms of absolute dimension and repeatability.
8. Any special operations - screw cutting - boring between centers - milling - dividing - power tool holder - braking and motor horse power - etc.
9. And last but not least the cost sensitivity of the build.
I suggest you start scoping out the head stock bearings and the truck sizes for the Z axis (bed). I think the bed stiffness and the truck sizes along with the head stock bearings will start to flesh out your design and build costs.
As a teenager I built a wood working lathe by building a temporary head stock using a pair of large plumber blocks (I think these are now known as pillow blocks ) to support a long shaft that was used to power a home made boring bar. The bar being threaded through the roughed out final head stock and supported by the tail stock. This enabled me to make a good head stock out of standard sized metal bar bolted and dowel pinned together to make the bearing supports and leaving room for a pulley system between the bearings for the drive. I managed to get the spindle machined at the school I attended during the lunch hours thanks to a friendly lab assistant.
There is one hell of a thrill to be had from a complete self build when you get to the end goal of making parts for something other than the lathe,
Hope this helps - Regards - Pat
Last edited by wildwestpat; 05-26-2011 at 03:16 PM. Reason: pillowbocks equivalent of plumber blocks of old?
hi
look for taper bearing used in vehicle
I have, but I wasn;t so sure that I didn't want to go with angular contact not taper roller. Angular contact are good in both radial and axial loading not so much with the taper rollers. Thanks
Does it make more sense to build a bed or to cut down one on a lathe and then attach the rails on top?
You would IMO achieve better rigidity by making use of an existing machine bed if you can find one of the right size. It would be difficult to fabricate a four foot bed stiff enough for a four foot lathe with a 4inch spindle.
Taper roller bearings would be as rigid if not more so than angular contact but they will have a lot more friction torque. Also 4inch /100mm bore is getting bigger than the common sizes for auto use. Suggest you might consider using deep grove ball bearings unless you are looking for ultra precision as these will stand considerable axial loads and a by pre-loading the shaft the float would not be an issue. Again look at the bearing manufacturers data both SKF and FAG have on line calculators to help you once you know the axial and radial loadings. Also shaft speed will also decide if taper roller is going to be a runner as these bearings are the province of high radial and axial loads at relatively slow speeds.
Don't get hung up on bearing type until you have worked out the load and run out tolerance for the spindle and the maximum RPM. A/C bearings come in several grades and the matched pairs should be avoided unless you are going high speed as they are very expensive. Matched A/C bearings are for mounting clamped together in packs of two or more with the pre load determined during manufacture - again look at the catalogues rather than the stockists web sites for information. Also note the quoted RPM is the maximum and is de-rated with load and life expectancy.
Good luck - regards Pat
As a design concept does a cnc turner headstock need to be much more than a pedestal and a tube ? Linking to ebay bites as this listing disappears in 9 days but here's the link anyway:
Hardinge Superslant Lathe CNC Turning Center SPINDLE | eBay
It would be easy enough to get something welded up that looks like that Hardinge piece but there would be stresses introduced and a million other details needed to finish it. Grizzly sells parts for their house brand lathes but the prices are a bit of an ouch, If you're lucky(??) enough to live in a major industrial area who knows what's available with a bit of hunting ? Here in the tundra it's like waiting for manna to fall from heaven. I may build a 7" with littlemachineshop parts after all.
Anyone who says "It only goes together one way" has no imagination.
The more I think about this project the better/worse it gets. I think I might do a small lathe with a donor headstock first and if I like it I will maybe start on a big one
Now I get more and more frustrated when I think about the big one. I still don't under stand why I can't make it smaller and lighter and still be accurate. I have seen 10 inch lathes holding 8 inch pieces of steel going to town on them. I only want to turn a 3 inch piece I just want to have the capacity to stick it through the headstock. It won't be 10 feet long its just what I want so I started some drawings.
The casing is 12Lx12Wx16H in inches. The bearings are 120x44x215 in mm. The spindle is 120mm OD with a 80mm bore. The faceplate is 10 inches wide. Now if I bolt this to a bed and throw some linear rails on it what would be my downfall when turning a 3 inch piece of steel? Rigidity? I can't imagine that you could shake this thing very well.
Definitely going to be thinning it out some as i don't see a need for some material, but this was a quick mock up. If it was all made of 1020 steel. Random choice, the spindle would weigh in at 55lbs. And the entire unit would be close to 450. The casing would all be bolted together. I don't know is this just screwed up or is it quite possible? Thanks guys.
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