Turning Using Tailstock Center For Support Is P***ing Me Off

[Kernbigo]

The last cut should be only .001 on something the springy

 

[cvairwerks]

You may have to improvise and use a sanding stick for the last few thousandths. Checking a couple of the online speeds and feeds calculators calls for a 6K+ rpm for a piece .190" in diameter. I would bet that you are running way slower than that and taking too much cut.

 

[tomw]

Dear All,

I did a turn between centers using 3/8" diameter brass stock, 2.5" in length. I used a dead center in the tailstock and a lathe dog and center in the headstock. All surfaces and tapers were clean, I used a newly sharpened HSS toolbit with an approx. 1/32" nose radius. I used a loupe to set the tool height to exactly center as compared with the center in the headstock. I took an initial .005 cut, then reduced that to .003.

The diameter of the part was measured at the closest point to the headstock and at 1.5" from the headstock. Dimensions were measured with my Mitutoyo 1" micrometer (digital, model IP65). The measured surfaces and measuring surfaces were cleaned prior to taking measurements, and the micrometer was zeroed. I used the ratchet mechanism to tighten the ram against the part being measured.

I got a taper of .0065 over 1.5".

I bought the adjustable center from Sherline (part number 1201)

After 6 hours of on again/off again futzing around, I got the taper, measured over 1.5", to .0002. WHOO HOO!!! Eff Yeah! I can now make my part!

My conclusion: the tailstock is very far from being accurately positioned relative to the headstock. Whatever measurements they did at Sherline when I sent the lathe back were not adequate, or it was upset during shipping in the exact way it had been off before sending it to them.

Thank you again for all of your help. I have learned more about lathe centers and center alignment than I ever had known I would need!

Cheers,

Tom

 

[Tozguy]

As already said, it is handy to have an adjustable tailstock center so that you can turn a taper on purpose or turn a dead straight cylinder on purpose. An adjustable boring head that fits in the tailstock quill would be another way of compensating for a non adjustable TS.

 

[kwoodhands]

Dear All,

I am having a frustrating problem. I can't turn between centers without getting a taper.

Here is the set-up:
1) Sherline lathe 4400, purchased in February 2015. This lathe was sent back to Sherline for adjustment of the tailstock (which was off a bit). Sherline reports the tailstock is now very well aligned.

2) I want to make a shaft that is 2" long, with each end being .19" in diameter for .19". The intervening diameter (between the two .19 diameter ends) should be approx. .09" in dia. This is thin enough and long enough that I need to turn this using a center in the tailstock.

3) I am mounting a 3/8" dia brass rod in a three jaw juck. The rod is center drilled on the outboard end (drilled with the stock snugged up short in the chuck) and extends from the chuck about 2.25 inches. A live center is mounted in the tailstock, and this is snugged up against the outboard end of the stock and locked down.
View attachment 107529
4) I then attempt to reduce the stock to .19 diameter over most of this length. I am using HSS, turning at 2500 rpm. I am getting no chatter. My final pass is .005 DOC.

The problem:

When I turn a bit of 3/8" brass rod stock between centers to bring to down to .19, I am getting a taper of .06 over the 2" that I am turning. So, if the end of my shaft in near the chuck is .190, the other end will be .196. The tolerance on the part, for the ends, is .002. So, I'm sort of screwed. Yes, I could swap the thing around and machine both ends close the chuck, but then there is no guarantee that they will be concentric, which will be important for later machining operations. Plus, this seems wrong.

In the below photo I am showing the diameters at points 1.5" apart to correspond to the next test (see below)
View attachment 107530

To see if the headstock or chuck are misaligned, I took a piece of .75" dia aluminum, approximately 2" long, chucked it in the lathe, turned it down down to around .5". Again, my final pass was .005 DOC.

Over 1.5" I am getting 0.000" of taper.
View attachment 107531

My request:

Please look over the photos of my set up and tell me what I am doing wrong.

Thanks,

Tom

Tom, seeing that your TS is not adjustable,make the center adjustable.Either use a boring bar holder and a 60° point instead of the cutter or make an adjustable one. There are plans on the web for this.I use a boring bar holder myself.
I hate realigning the TS after turning tapers that's why I use the boring bar holder.
To align the point,use a round that is center drilled on one end and a 60° point on the other,mine is about 8" long,length not critical.The point sits in the center drilled work piece and the other end that is center drilled goes into the dead or live center in the TS.Now install an indicator on the tool holder. Take readings at the #1 and #3 scrolls.
Add the two readings and divide by two. This is the correct reading for the #1 and#3 scrolls.Repeat for #2 and #4.
I'm assuming you are using a 4 jaw chuck.Repeat this process until you are satisfied the work is centered.
Any taper should be negligible,probably less than your ability to measure.

mike

 

[planeflyer21]

Hunt around this guy's channel, as he's doing his lathe work on a Sherline also. One of the vids I remember him adjusting the headstock to cut tapers. It may have some useful info:

https://www.youtube.com/channel/UCworsKCR-Sx6R6-BnIjS2MA

 

[Wreck™Wreck]

The diameter of the part was measured at the closest point to the headstock and at 1.5" from the headstock. Dimensions were measured with my Mitutoyo 1" micrometer (digital, model IP65).

IP 65 is an Ingress Protection Rating issued by the IEC for electrical and elctronic devices, basically how liquid and dust resistant said device is. You may not have a good deal of experience running a lathe with flood coolant, coolant ingress will cause serious problems with unprotected electronic digital micrometers, calipers and indicators.

IP also covers electrical enclosures, the "ingress" of body parts into the conducting surfaces of terminal connections on motor starters, relays, terminal blocks and timers and so on.

 

[4GSR]

Your bed has a slight twist in it. If you have it bolted or screwed down to a piece of wood or bench, loosen the screws at the tail end of the bed and see if the problem goes away.

BTW- the co-axis indicator is not the correct way to check alignment between the headstock and tail stock. There is one and only one correct and accurate way of checking alignment.

 

[tomw]

Ken,

I am not sure what you mean by Co-axis indicator. I used a micrometer to check for taper, and visual inspection of the centers to look for misalignment.

I will check to see if loosening a hold bolt makes a difference. I was already thinking about bolting the lathe to a machined flat chunk-o-steel.

Thank you all for your help with this problem. The adjustable center solved my turning problems. Using the mill has solved my drilling problems (for now).

Thanks again,

Tom

p.s. Mike, I just read your post carefully. Sherline makes an adjustable center, so you technique isn't needed. However, I can think of several uses for it, so thank you for posting that.

 

[kwoodhands]

Dear All,

I am having a frustrating problem. I can't turn between centers without getting a taper.

Here is the set-up:
1) Sherline lathe 4400, purchased in February 2015. This lathe was sent back to Sherline for adjustment of the tailstock (which was off a bit). Sherline reports the tailstock is now very well aligned.

2) I want to make a shaft that is 2" long, with each end being .19" in diameter for .19". The intervening diameter (between the two .19 diameter ends) should be approx. .09" in dia. This is thin enough and long enough that I need to turn this using a center in the tailstock.

3) I am mounting a 3/8" dia brass rod in a three jaw juck. The rod is center drilled on the outboard end (drilled with the stock snugged up short in the chuck) and extends from the chuck about 2.25 inches. A live center is mounted in the tailstock, and this is snugged up against the outboard end of the stock and locked down.
View attachment 107529
4) I then attempt to reduce the stock to .19 diameter over most of this length. I am using HSS, turning at 2500 rpm. I am getting no chatter. My final pass is .005 DOC.

The problem:



When I turn a bit of 3/8" brass rod stock between centers to bring to down to .19, I am getting a taper of .06 over the 2" that I am turning. So, if the end of my shaft in near the chuck is .190, the other end will be .196. The tolerance on the part, for the ends, is .002. So, I'm sort of screwed. Yes, I could swap the thing around and machine both ends close the chuck, but then there is no guarantee that they will be concentric, which will be important for later machining operations. Plus, this seems wrong.

In the below photo I am showing the diameters at points 1.5" apart to correspond to the next test (see below)
View attachment 107530



To see if the headstock or chuck are misaligned, I took a piece of .75" dia aluminum, approximately 2" long, chucked it in the lathe, turned it down down to around .5". Again, my final pass was .005 DOC.

Over 1.5" I am getting 0.000" of taper.
View attachment 107531

My request:

Please look over the photos of my set up and tell me what I am doing wrong.

Thanks,

Tom

Tom, the quill with your live center may be adjusted too tight.Possible you have slightly bent the shaft.Adjust the quill so the live center just turns,you may have to readjust with use.
mike