What's new
What's new

Request for Help with Custom Lathe Headstock

Status
Not open for further replies.

hardwiredsoul

Plastic
Joined
Apr 15, 2024
Location
U.K.
Hi all,

Sorry to ask for help on my first post! I’m building a small, specialist lathe type machine in my garage and seem to be having some issues with it.

I’ll attach pictures but in essence I have a VSM direct drive, (14mm keyed shaft output) which I have used a rigid coupling to couple to a stainless steel 40mm keyed shaft with a pillow block for support. This is cantilevered maybe 150-200mm and I’m seeing some large “deflection?” At the end of approx .5mm, any ideas why?

I may be missing something obvious as I’m no engineer, happy to pay for consultancy if necessary, based in the U.K.

Thanks in advance, Danny
 
Last edited:
I'm not an expert, and I'm certainly not an engineer, but I wouldn't expect much better results with that sort of setup. What sort of runout do you get right next to the coupler? Keep in mind that pillow blocks aren't the same as a set of precision headstock bearings with adjustable preload so you aren't going to see results like you would with a lathe. Then add the long unsupported shaft and things are going to multiply quickly.
 
I'm not an expert, and I'm certainly not an engineer, but I wouldn't expect much better results with that sort of setup. What sort of runout do you get right next to the coupler? Keep in mind that pillow blocks aren't the same as a set of precision headstock bearings with adjustable preload so you aren't going to see results like you would with a lathe. Then add the long unsupported shaft and things are going to multiply quickly.
Perhaps just buying an old lathe headstock would be the route to go down then?

The runout next to the coupler and next to the pillow block bearing is 0.1 give or take.

I based the machine very loosely off a wheel balancer which also features a 36-40mm cantilever shaft.
 
Shaft needs two bearings, spaced apart as much as possible. Get rid of rigid coupling, replace with appropriate style.
I have tried to go down this route. I mounted the motor lower and used a pulley and belt system with 2 pillow blocks, unfortunately didn’t really work either.
 
.5mm deflection under what load and in relation to what?
You have several slip connections and low precision bearings all mounted on a bolted together aluminum extrusion frame.

All the joints have clearance that will when loaded will deflect and add up,

The second picture with the 2 bearings is a better design as far as the main shaft support but is attached to a plywood frame that will flex quite a bit. and even this could have the bearings further apart for even (100mm+?) better support

But as said above these are not precision preloaded bearings pressed onto the main shaft and mounted to a rigid frame so runout and deflection numbers will never be what most would consider good.
 
Try harder? Why didn’t I think of that before…

Something along these lines?

View attachment 436259
Given your setup 20 thou of deflection isn't surprising. The second setup looks better except for the part where its mounted to wood..

As for the try harder comment I agree - try harder telling us what you are trying achieve and you'll get better advise. And edit the thread title to something descriptive - Request for Help with Custom Lathe Headstock.

If you're making a generic lathe in your garage because you don't have the budget to buy a real one you aren't going to get any positive feedback on a professional machinist forum, you'll be best suited over on hobby forums. If you are making a custom lathe for a dedicated application that a typical lathe isn't optimal for tell us more about what you are doing.
 
Given your setup 20 thou of deflection isn't surprising. The second setup looks better except for the part where its mounted to wood..

As for the try harder comment I agree - try harder telling us what you are trying achieve and you'll get better advise. And edit the thread title to something descriptive - Request for Help with Custom Lathe Headstock.

If you're making a generic lathe in your garage because you don't have the budget to buy a real one you aren't going to get any positive feedback on a professional machinist forum, you'll be best suited over on hobby forums. If you are making a custom lathe for a dedicated application that a typical lathe isn't optimal for tell us more about what you are doing.
Yeah I agree re design and re not mounting it to wood.

If I can figure how to edit the title, I will.

Thanks for your feedback and help, budget isn’t a constraint, simply put a standard lathe isn’t optimal as my workpiece will be 600mm diameter give or take a few mm’s. I understand now pillow blocks should always be used in pairs so I’ll go back down that route and see where it gets me :)
 
Yeah I agree re design and re not mounting it to wood.

If I can figure how to edit the title, I will.

Thanks for your feedback and help, budget isn’t a constraint, simply put a standard lathe isn’t optimal as my workpiece will be 600mm diameter give or take a few mm’s. I understand now pillow blocks should always be used in pairs so I’ll go back down that route and see where it gets me :)
they make lathes that can handle 600mm diameter workpieces, if budget is not a constraint I/we don't understand the need to seemingly reinvent the wheel. What are you trying to accomplish that you must start from raw materials to achieve? Perhaps someone in the community has some advise on how to accomplish the end goal more efficiently.
I feel as though you are asking how to catch tuna when all you really want is a tuna fish sandwich and are unaware of the canned variety.
 
Is your shaft straight, true, and concentric to begin with? Looks like that one has traveled over a shop floor once or twice and been traveled over itself by some heavy blunt objects. You can not check the runout of a shaft in bearings unless you know the shaft to be near perfect before mounting it. If you have access to a lathe mount it between centers and verify your shaft is good.
Also... a single "pillow bearing" is not a rigid setup for a true running shaft. There is some flexibility built in to it. As others have said... you need at least two bearings. Most spindle setups (lathe or mill or grinder or whatever) have at least two 'angular contact' ball bearings and.sometimes a couple more to keep the outboard end from flopping around.
 
Unless you are turning butter, that direct drive setup is not going to have the torque required to turn/cut something 23" diameter. If you need a lathe that will turn 23+" diameter, and fit in your garage, look for a Standard Modern 26x30, there is probably a few other makes out there.
 
likely somone told you the 1/2 distance to the one bearing. and then the full distance out what error you have at the motor will be double at the far end.

If you put on two bearings then the shaft will/may run true and you may have a big vibration where there is error at joining the motor.
QT Op: (I mounted the motor lower and used a pulley and belt system with 2 pillow blocks, unfortunately didn’t really work either.) ->Perhaps that shaft is not straight.
*Plus..what RPM are you trying to run?
 
Last edited:
You edit your title by editing your first post. Look near the top and you'll see the title box, which you can edit for up to 24 hours. If it's not edited to be more meaningful, the thread will be locked. This is in the rules and guidelines, which you should have read before posting...

 
600mm 24 inch even in wood is a big dangerous part, likely you should have a machie of 1000 pounds or more for lathe turning a part that big..
There are safer ways to round and shape a part that big. Some times a big part turning slow and perhaps a cutter turning fast can be safer.
The guys here could be more help if they knew more about the part.
 
QT (Thanks again to everyone for your help and input; I gather the best route to go down is a brand new 40mm shaft from hardened steel, and another pillow block bearing)
No, the best rout is to tell what needs to be done and designe a something that can do the task.

Gussing from here you may need to shape something that is 24" in one measurement.
 
Last edited:
Status
Not open for further replies.








 
Back
Top