Tailstocks on Tri-Power

[TomB]

Has anybody ever thought about putting a different tailstock on these machines? I had to turn down a big shaft last week and to support the tailstock end without using an extension I had the table travel trapped between the headsock and tailstock with only a 1/8" of clearance at each end of the travel. Even then the tailstock was fully extended and it did not provide much support. I tried using the support thing but it did not line up with the tool so I had to mount it when the cut was started at the tailstock then stop part way through the cut to remove it, otherwise it would have hit the chuck.

I looked breifly at putting the tailstock on backward but the tailstock spindle can't mount to the front side and if it could it would only buy a couple of inches.

What I would have liked is some sort of tailstock that would reach over the table about 6 inches. I though about making something that could interchange with the top part of the existing tailstock, but before I got into welding and cutting I wondered if there was enough tailstock to ways lenght to keep such a part stable. That said, it occured to me to ask if anybody else had thought through this option.

Tom

[instructor37]

Tom,
What is the diameter and length of the part, and how much do you need to turn. This is one of those things I like to throw at the students to see if they can come up with a solution.

[TomB]

I started with a solid cold rolled steel 3 3/4" diameter by 10.75 long. (It actually will need to be faced down to 10.50 but I have not got that far.) I mounted it in a 3 jaw chuck supported the end and center drilled it. Then with the stock running in the chuck at one end and a 'live type' center in the tail stock I proceeded to turn down 10.15" of length to 2" diameter. I needed and left a .6" thick flange in the chuck that will eventually be faced down to .5"

First I'm not very good at griding tool bits so I always ended up with a spiral cutting trace. Usually I get it close then remove the spiral with a grinder. But on this part I could not even get the diameter close. It would chatter so bad at the tailstock end that the finsih looks to have .005" roughness, but them about 1/3 of the way across the cut it smooths out and by the time I got to the headstock it looks like my normal spiral. Just for kicks I tried stopping berfore I got to 2.25 diameter then grinding to hit that target. I could not get even close to a constant diameter. At this point I'm just bigger in all dimensions than I need to be and it is going to a machine shop for finishing,

If I get a chance tomorrow I'll remount the part to take a picture that can be posted tomorrow night. However I have the vice on the machine right now and don't know if the milling will be complete before the day is out.

Tom

[dgapilot]

Tom,
Sounds like either your tailstock isn't on center, or you have way too much overhang for your tool. Another problem could be the gibs on the cross slide are a little too loose. Rigidity is your friend!

Measure from the table to the center of the spindle, then measure from the table to the center of the tailstock. If the tailstock is high or low, that will cause your tool to be off center and chatter. Another way you can check this is to put centers in both the spindle and the tailstock. Bring them together with a piece of aluminum sheet in between. When the centers contact the aluminum, the sheet will stay perpendicular to the table if both centers are in the same plane horizontally, and perpendicular to the bed if both centers are in the same plane vertically. If the sheet swings to one side or tips, your centers aren't lined up and you will never get a good part.

Hope this helps.

David

[smallblock]

For a part of that size you definitely need a solid tailstock support and also follow the pilots advice to make sure its aligned properly. Also, make sure your compound is tight as well- I removed the center gib adjuster on mine and replaced it with a small lock handle, so I can lock it solid under heavy loads. The width of the cross slide table on a 3 in 1 machine make it a challenge doing long turning in 1 pass. Because the table can pass under the chuck, I would set my compound in the center or right groove in order to get as close to the tailstock as possible and reduce the amount the barrell is extended. With a little setup, you can mount 2 tools in the compound and when you need more travel, rotate the center block 90 degrees- this will give you about 5" more travel. If you plan another of those parts, consider starting with a longer piece in the beginning so you can utilize your full travel, then cut away the excess.

[aisrad]

If you remove the DRO cover on the left side of the carriage, you'll gain over an inch.

[TomB]

Originally Posted by dgapilot Tom, Sounds like either your tailstock isn't on center, or you have way too much overhang for your tool. Another problem could be the gibs on the cross slide are a little too loose. Rigidity is your friend!

I have looked pretty closely at those things.

Early this summer when I started using the machine for a significant project (previousily I had made special washers, push pins for the press, adapter parts to hold dial indicators and similar small stuff) I actually used bluing to measure how gibs fit the dovetails. It was not pretty and I spent several days with an Arkanass stone to improve things. I'd still like to further true things but it requires a surface grinder and mine is not running yet. As things now stand the cross feed table has sticky spots in the travel but it locks tightly and I can't measure any looseness when I try to twist it with an indicator measuring between the table and the lathe ways. I've also put two rigid centers in the lathe and then pinched my 6" machinist rule between them. I found the axis of the headsotock and tailstock does not quite line up. I adjusted things so they are best when the tailstock is half extended.

As Smallblock says I was struggling to fight the width of the table. I was using 1/2 x 1/2 " HSS bits mounted on the left of the compound block. I use the plith and 4 sided block that came with the machine so there are no gibs in it. I ground the bits so that they could be rotated into the cut about 20 to 30 degrees and extended them about an 1 1/4". That meant the bit was engaged while the trailing edge of the compound block was just clearing the pin being cut. With that setup and without using the tailstock extension I could get the bit to clear the right end of the part by about a 1/16" while the lock crank on the table cross feed cleared the tailstock frame by 1/8" - if the tailstock was almost fully extended. I could not actually square the bit more to the work because when the cut got to the headstock I was within a 1/16" of the end of the travel.

What I was wonding about was basically a direct attack on the width of the table. I'd start with a 10" x 2.5" by 2" steel block and mill the grove and cavity so that it would fit on the base of the current tailstock. Then weld some 4inch channel to the block so that so the channel reached 6" across the table with some room to reach the cross feed lock. Finish with a 3/4" thick plate across the ends. Something like the attached sketch. (The spindle would be about a 1/4 lower than shown but I did not try to measure it carefully.) But what I was wondering about was the stiffness between the tailstock base and the ways. If the spindel was move that far inboard would the whole tailstock want to rock back even when locked?

[instructor37]

Originally Posted by instructor37 Tom, What is the diameter and length of the part, and how much do you need to turn. This is one of those things I like to throw at the students to see if they can come up with a solution.

Tom-
I threw your problem out to the students to see what they would come up with. Part of the deal was that anything they built had to be done on the machine itself. I got some pretty good ideas.

1. One idea was like yours- to build an extension over the carriage to hold the tailstock assembly. His idea was to use an existing product like a cast iron angle plate to reduce fabrication time- you would only need to bolt it to the existing base and bore the hole for the tailstock assembly with the lathe, giving you the proper horizontal/vertical alignment.

2.- The second idea was a bit radical but clever. He suggested using the same type of existing angle plate, but bolting it to the steel support bar that is attached to the mill head. This would give you a " hanging " tailstock which would free up another 5-6" of travel for the carriage.

3. This student had a similar idea as smallblock- just begin with a longer piece and work the center to dimension and then cut away the excess-

4. Another student figured the simplest solution based on your material description and also figuring you don't want to start all over, was to tap the end of the piece for a 1/2 -20 thread and use a piece of threaded rod as a drawbar in the lathe spindle. By pulling the piece tight up against the chuck face with the drawbar, any deflection in the cut would be limited to the chuck runout, as your piece is probably not going to have a lot of deflection in itself.

I figure that students 1 and 2 will trend toward engineering, while 3 and 4 have that practical machinists attitude of looking for the simplest solution to a problem.