[breathe]

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.

[RotarySMP]

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?

[breathe]

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?

Hmm thought I replied, but I guess not.

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?

[cyclestart]

Just wondering. not sure if I want to build the whole headstock myself or if I am going to find a salvage one somewhere

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.

[rowbare]

Do I really need a 1/2 wall thickness. That seems pretty huge. I guess I am not planning on hogging anything.

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

[breathe]

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?

[wildwestpat]

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

[hesham morsy]

hi
look for taper bearing used in vehicle

[breathe]

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?

[wildwestpat]

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

[cyclestart]

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?

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.

[breathe]

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.

[RotarySMP]

Build it.

If you access to a decent size lathe with a steady rest, go for it.

Small lathes typically don't have this sized bore. If you want this size bore, go for it, and please post lots of photos. Will be a cool lathe.

[wildwestpat]

You need to consider the forces that will be generated on the bearings. Do we assume that the billet of metal to be turned is over hanging at both the face plate end and at the rear of the head-stock? If so the over hang imposes a load on both bearings and as the billet whips as the speed increases the forces will be large and you could well excite resonances in the plate construction of the head-stock which would also transfer to the bed and hence to the tool.

For through bore head-stocks it is normal to have a secondary chuck and probably remote steadies to control the billet as it rotates. You have given no details on the size of the envelope you which to machine (diameter and length) and the length that is passed through the head-stock.

Rigidity has a twin sister in resonances that are excited. In general the bigger the machine the more attention has to be paid to resonance.

Have you considered machining between centres?

The trucks for use on those HSR25 rails have a limit on the forces that can be applied so you need to asses these in terms of tool cutting force on the carriage as well as their contribution to the general movement under load. Again as the balls ride up the profile they act as a spring and reduce rigidity. You need to go round the accuracy - rigidity - resonance loop several times as each has an impact on the other two with cost acting as the final litmus test.

Sorry but you need to do the sums unless you like experimenting in which case run up to speed with caution!

With the cost of the materials and bearings for the head-stock at around $1000. With lead screws - motors etc you will be rapidly approaching the cost of a good second hand machine.

Regards - Pat

PS A lathe of this size is too big for most home workshops so you are talking scrap or second user prices not the premium pricing that attaches to small machines that are better suited to the average small workshop.

[breathe]

Jet JWL-1236 Lathe

Any reason not to use a wood lathe like this as the base. I mean if I am just going to take all the lead screws off and replace them and will be using linear ways instead of dove tail wouldn't this make more sense? I mean I could obviously find a heavier duty on, but its seems reasonable to me.

[cyclestart]

The wood lathe bed looks like cast iron but it's hard to tell how thick the castings are from the picture. Fully supported it may prove plenty strong.

The bolt together head stock could use some dowel pins to prevent shifting. If it is bored in-place (line bore) aligning the bores would be easier. Getting a setup to bore in-place would take a bit of planning and ingenuity.

[wildwestpat]

Could be a good start. However you will still have a lot of work to do:-

1. The bed should be OK as a donor but will require checking to see if the top face is flat enough for the precision you need.

2. Guides for both the new saddle and the tail-stock will need to be sorted out. That central gap may only be rough finished as this is not critical for wood-working. (I have seen round ground rods with fixing holes every 4 inches which might fit to one side and engage with a 'Vee' grove in the saddle and tail-stock. A 'Vee' grove in your new saddle and the tail-stock would then ride on the circular rod. The guide system is a major contributor to the rigidity of the tool post. The bend of the bed between the supports could be measured as this will determine if the bed is strong enough. A metal working late has loads of cross bracing a wood working lathe little in the way of cross braces as the tool rest needs to be adjusted quickly along the bed and is held in place with a through bolt in the gap between the two slides.

3. The headstock bearings may be OK but you may need to make an accurate adaptor plate to take the back plate of any chuck you may wish to attach. This is because the demands for wood turning are different as the job is normally turned all over and the concentric accuracy of the spindle is not a big factor. The headstock will probably need shimming to align it with the bore of the tail-stock after you have fitted the guide system. Provision to bolt down the headstock needs to be investigated as there may not be sufficient metal to permit bolts in the four corners or similar for tapped holes. Dowel pins a good ides once the alignment is sorted and the shims are in place.

4. Is the head-stock spindle bore big enough for you? Again the demands of a wood turner are for spinning a large lump of wood and this requires a thick walled spindle. I think the bore is 3/8 inch.


Good luck - Regards - Pat

[llilrex]

on the subject of the headstock, if I were going to make a lathe (I probibly will) I would use tapered roller bearings for the head stock. you do have a penalty in speed but they are inexpencive when buying them in semitruck sizes. they are not percision so to speak but are good quality and very cheap (they are used in DOT regulated vehicals).

as to the applicability of tapered bearings? well I have a colchester clausing Mastiff, it is a 21" x 120". and though it is much bigger then the machine you are making (8000 lbs) it is a good example of a quality machine that uses tapered roller bearings. I have a cheap harbor freight lathe that uses tapered roller bearings too.

the bore to my mastiff is a little bigger then 3.5 inches its bearings are probibly 6 inches inside diameter. and it easily handles 1400 RPM, at 12.5 Hp.

your spindle will certanly not require the stoutness of the mastiff, so you would not need such bulk. I would look into timken bearings, the 594A has an ID of 3.75 inches and costs $28.12 from class8trucks.com timken 687 has a ID of 4 inches and and OD of 6.625" but is a little harder to find. but you can still get it around $80.00.

amazon has the timken 780 bearing, its dimensions are 4.000" x 7.125" for $96.65
note: this bearing inner cone is part# 780, its outer race is part# 772

I have attached a drawing of the 780/772 bearing set.

[breathe]

Looks like this project is going to go on hold. I just picked up a 36 inch Bridgeport kneemill. Spend several hours just wiping grim off of it. Now I am going to need to get some more tooling and build a high pressure oil gun. Anyone have the reccomended oils for all the lube points?

Also the place I got the mill had a clausing 1500 lathe. What is the value on that? Some tooling. Again pretty grimy. Under the grim the BP is looking pretty nice though. Should make projects go much fast vs running to the school when and if they are open and I have time.

Thanks guys. Hopefully this will come back, but I don't have the money to put towards it anymore. I got a nice piece of american iron instead

back at some point :wave: