I am turning between centers on my lathe and I'm getting tapers in my cuts when cutting over long distances. Basically the final piece is wide right at the main chuck side and smaller at the tailstock end. Why is this? How do I align the lathe so it cuts true parallel?
Hmm. I will check. Its very subtle. Over about a foot and a half its off by maybe 5 to 10 thou. If the tail stock is off it cuts tapers right? Or could something else be wrong?
5 to 10 thou over 18 inches is not that bad at all. You can start by trying the "two collar test" where you machine a test bar in the lathe while not using the tail stock at all. You machine two identical diameters on either end of a bar say 1" diameter or larger and say 4-5" apart. This lets you align the lathe bed to eliminate any bed twist in it's mounting so that the collars machine to the same diameter ideally. You have to use a sharp point tool to minimize deflection while taking light skimming cuts with a slow rate of feed. Once you're happy with the two collar test, you can mount a dial indicator on the end of a test bar in the lathe chuck and use the indicator tip to measure the morse taper socket of the clamped down tailstock to see just how far off center axis the socket is. Usually the base of the tailstock is worn and the tailstock is lower than the center line, it's possible to temporarily shim the tailstock base to compensate for wear. I made a two collar test bar by getting some machined 1.5" steel bar and Loctiting two 3" x 0.5" thick aluminium rings/doughnuts onto the steel bar about 4" or so apart.
Search YouTube for "Lathe Leveling" & Lathe Two Collar Test". There will be zillions. Select you favorite......MrPete/Tubalcain, This old Tony etc. If you have a machinist's level, that can help converge a little more quickly. Also, how is your lathe mounted? If it's a light duty lathe on a wooden bench or tool cabinet with casters, it will be very difficult to impossible to get it dialed and keep it there. Most would recommend a stiff stand anchored at four corners into a concrete floor. I didn't anchor mine but have a stiff stand/cabinet with a lot of weight in it. Can make a big difference with a light lathe. Best, Kelly
My lathe deflects badly, I get chatter when cutting more than about 3-4 inches from the chuck without using the tail stock. I think there must be some wear in the bearings of the head stock or something. I'll have a look and see if I can figure out where the wear is. Probably under tail stock as you say. How is the tail stock shimmed? Doesn't it slide on the ways ? Where does the shim go/how is it attached under tail stock so it doesn't slide out off the ways? The lathe is just sitting on the concrete floor. I did notice when cutting a 4 foot pole there was a lot of twist in the lathe bed. I felt it vibrating due to not being bolted to the floor. But didn't feel that over the smaller 1.5 ft distance. The cabinet is pretty heavy. About 1890 lbs total for the lathe (old south bend 13 inch tool room O series).
A garage floor will never be level enough for a lathe with out shimming the feet and then the lathe. The weight of the lathe and stand itself can be enough to deflect the bed on an uneven floor, and "uneven" for a lather is a very small amount, far beyond the precision of working concrete. The farther the cutting is from the headstock, the less rigid the bed becomes. The reason anchors are recommended is because high cutting forces and low weight can actually lift a corner but not if anchored. Best, K
I believe it. I felt the lathe bed trying to torque when I was cutting that 4 ft pipe for the ruby machine post. Would a different lathe design remove this issue? Say for example a monarch lathe or other newer design? It looks like a lot of them are braced along the floor as well rather than supporting the bed with 2 little dinky legs. I'm guessing that improves rigidity. At some point after I get a mill I'd like to upgrade and get a beefcake lathe, I like the look of monarchs but am open to alternative lathes. Something with power and decent ways. I really feel that my south bend has no cutting power. The little dinky 3/4 hp motor on it can barely handle cutting through 10 thou cuts. It takes me ages to turn down a piece of work. I'm talking 2-3 hours of dozens of tiny cuts at a slow speed or it stalls out. It's painstaking
Machine rigidity is a key element and it doesn't come without more metal mass. -Big toys for big boys. Best, Kelly
I will plan to increase the tonnage in the near future! As for now I'll tinker with the tail stock and see what I can find
I'm a bare novice so take it for what it's worth, but the right tooling (sharp high speed, fresh carbide insert edge, correct angle of approach, etc) as well as the right spindle speed for the alloy and tooling type goes a long way toward increasing your productivity. I am listening carefully to what our more skilled members are sharing here, especially when it comes to more massive work but when even small pieces are eating my lunch on my little SB9 it's usually because my setup or tooling isnt right. Once I get that squared away the improvement is often dramatic. Pete
So true. A properly ground sharp tool makes a big difference........but it also does on a bigger more rigid machine. Best, Kelly
Hmm. I've tried several hss bits freshly ground, fresh carbide inserts and different angles. Still seems to be a hard limit to the depth of cut I can take before the lathe/leather belt stalls out. Putting belt conditioner on helped increase the power a bit but it still feels underpowered compared to what people are doing on YouTube. To be honest I haven't played with speed a lot, I generally tend to cut on the slowest speed I can since that seems to allow me to cut deeper than a hundred hair thin passes on a faster carriage speed. I will have to play with speed more to see if that helps.
I'm limited by belt slippage with my SF lathe, switching from a leather belt to rubber reduced slippage quite a bit, but I would also look to setup and tooling as mine cuts well when I get things right.
Are you sure that thing is really level. I mean REALLY level with either a machinist level or a digital level? Next place I'd be going is checking headstock bearings. Tailstock can be suspect too. Mine slides on it's mount and is adjustable too. If you are really only seeing 5-10 thou over that 18" with your machine, I'd think that was pretty damn good. What do you see when you just traverse down a piece of ground rod held in the chuck.... NOT RUNNING...??
I'll have to check with the 3d printer rail I have. I think it has been ground and is 1 cm thick. I'm just guessing 5 to 10 thou, will see. Probably underestimating it.
Get yourself a nice piece of ground rod out of a cheap strut. https://www.ebay.com/itm/233069618158?fits=Make:Toyota&epid=20017086423&hash=item36440823ee:gzUAAOSwqTdgnEbC I dare someone to find me a cheaper solution than this 13buck shock! FREE SHIPPING TOO! Drill very small hole when fully extended, drain, then cut open and retrieve your prize!
I wouldn't disagree that is a good source of ground stock but you'd need to get it on a surface plate to ensure it wasn't made like a banana.
Linear race rod (also search liner motion rod) is a good source of turn ground and polished rod that is also very straight. McMaster wants $20 for a 5/8" by 1ft rod but you can source it on eBay and Amazon for $7 if you can trust the specs. https://www.mcmaster.com/linear-motion-rods/linear-motion-shafts-5/ Here's a seller you select whatever diameter and length you want. https://www.amazon.com/PDTech-diameter-bearing-hardened-251mm-500mm/dp/B07CYMNZBP/ref=sr_1_20_sspa?dchild=1&keywords=linear+race+rod+20mm&qid=1629894203&sr=8-20-spons&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzUFQ2V0Q5ODZCTkYzJmVuY3J5cHRlZElkPUEwNzQ4NTIzMlo3SlhPNUlNNjczMiZlbmNyeXB0ZWRBZElkPUEwMTIwNzc5VTJMWFo2MlZJOEk3JndpZGdldE5hbWU9c3BfYnRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ&th=1 I used a piece of 5/8" diameter x 12" race rod I had left over from a project because is was very round, straight, and a close tolerance diameter ready made to receive press fit aluminum collars. I pressed on two 2" diameter aluminum slugs and also bored and chamfered the rod from each end for between centers mounting. It's nice and it looks the part for a test bar but you don't have to have a close tolerance rod since you'll be taking light cuts on the collars for your test surfaces. A 2" collar provides lot's of stock for many cuts. It depends on machine condition and the amount of fiddling you want to do but FWIW, it's a very light duty 75 year old lathe, and without too much hassle was able to repeatedly achieve .001-002" on that 10" test bar but that's just at that particular location where the tailstock was clamping but I saw very similar results inside the 10". You can use a longer test bar but you may still see variation along the lathe bed due to way wear, how well the bed is leveled, the condition of your tapers, and how well the tailstock clamps and repeats. I chose 10" most because it fit the rod and was convenient and virtually all my close tolerance work would occur within that envelope but at least at that point you know the height of the tail stock is where it should be and the rest is tuning/leveling/shimming the bed if they ways are in decent shape. The ways on old lathes usually exhibit more wear close to the headstock, same with the lead screw, so you can have it dialed perfectly at the high wear point which may sit .00x" below the surface 12" down the bed. Of course all of this is most relevant if you are trying to turn a close tolerance diameter over the full length, but usually, if you just want concentric features at each end, like say bearing mounts on a shaft, all you need to do is be mindful the taper will be there and just measure and cut the two surfaces accordingly and not rely on you dials or DRO. How many times will you really need to cut over that length? You just need to watch some videos and invest the time to dial your lathe in. Best, Kelly
Well I noticed the issues when I cut the mast post for the ruby machine, the top is narrower than the bottom so the clamp rings I made have to be forcibly massaged to fit the bottom part. If I had known about it when machining it the first time I could have taken multiple small cuts down the length of the post to cut out the bulk of the taper. I'd like to replace the bearings in the head stock and put in new cross feed lead screws with a new split nut to increase the tightness of it. I find the dials don't seem to reproducibly cut the increments they state. There is a lot of slop in the screws. Some of that I can compensate for but sometimes it seems like there is a step off where the lead screw shifts during a cut even when the dial is held firm. Leads to somewhat unpredictable cuts. I mean its a 90 year old lathe with unhardened ways and I bet no replaced parts so pretty much its for roughing work, but it is still irritating I can't use it like I want to. I think I'll have to upgrade it one day. Maybe next year after I get a mill and a car. I think my plan for the mill is to buy a pretty much brand new or completely restored/reground/all new parts with no play in the dials or anything to fix. I don't enjoy fart assing around with a tool that I have to compensate for when I don't know what I'm doing with it half the time. Makes it difficult to learn and figure out if the issue is me or the machine.
