[pmurdock]

G'day,

got a Haas SL-30

so up until now in order to get accurate lengths on parts in my 3 jaw chuck I usually machine one end. then unchuck it and measure from the machined end to the length I need (then mark with blue dykem and scribe as best as I can with a vernier caliper) then rechuck it with the unfinished end out. Then I manually go in and try to get as close to my scribe as possible. Suffice it to say this is time consuming and there must be a better way!

I have seen that they have 3 jaw chuck stops (ie see royal products [ame="http://www.amazon.com/Royal-Products-25200-Piece-Standard/dp/B0037QG98G"]http://www.amazon.com/Royal-Products-25200-Piece-Standard/dp/B0037QG98G[/ame])

However these are only really good for short pieces.. Anyone have suggestions for a 3 jaw chuck stop that allows me to run long pieces and get accurate results quickly?

Could I run some all-thread through the backend of the spindle hole and use that as a stop? but then how to keep it from wobbling around. any other ideas?

cheers,
Paul

[Geof]

I think the problem with using the back end of the spindle is that it is actually the back end of the hydraulic chuck drawbar so it moves when the chuck opens. My lathes warn against attaching any stops to this location.

The only way I have ever figured out is to build a bracket off the back of the machine and attach a stop to this. The stop is just a length of bar with a plug that just fits inside the spindle mounted on a bearing. This way the stop can rotate with the spindle even though the bar is fixed.

[txcncman]

+1 to what Geof said.

Depending on part length and diameter, I have also machined adapters to fit into the chuck and threaded tubing of various lengths to create a stop.

Another method to use is to face both ends and measure length. Then put bar in check and touch off tool and set work offset zero. Then subtract amount needed to face off additional material from the work offset.

Final method is to set one tool as a stop and bring to known Z position and pull stock out to touch tool.

[pmurdock]

I'm not so sure the back of the spindle does move relative to the face of the chuck. I'll check it tomorrow - but the back of the spindle has a bolt hole pattern for attaching spindle liners (I've never used them before).

So perhaps this bracket can be made to attach to the bolt hole pattern on the back of the spindle.

I'm not quite grasping where the bearing would go Geof - in the bracket or inside the spindle - each with their own problems.

if in the bracket - then yes the stop can potentially spin with the spindle - but what keeps the rod stop from wobbling on the inside of the spindle and what makes the rod follow the rpm of the spindle.

if inside the spindle open bore - then the rod would be stationary while the spindle moves and mar the surface on the finished side of the part by rubbing.

I'll take a look at the machine tomorrow and see if I can verify if that bolt hole pattern face moves relative to the chuck. I know the hydraulic drawbar moves internally but I don't think that BH pattern face moves.

(see attached image 1)

to txcncman

thanks for the tips - these adapters though are not held in place by the clamping of the jaws - since the jaws will need to hold the part in place - how have you held them in place? I envision you could use those royal stops - thread a hole in there - screw in some threaded tubing (loctite it) and then have some ID threading on the other end to adjust the stop -

see attached image 2 - is this what you were thinking?

cheers!
Paul

[Geof]

I did a drawing.

The spindle has the chuck on one end and the hydraulic cyliner for the chuck on the other.

The draw tube is inside the spindle and connects to the chuck at one end and the hydraulic cylinder on the other.

On my machines the draw tube extends beyond the hydraulic cylinder, I think yours will be the same.

The draw tube moves when the chuck opens and closes so I (you) cannot attach a stop to it.

My stop is a bar mounted on a bracket attached to the frame of the machine.

The bar is fixed, but can be adjusted forward and backwards for different part lengths.

The stop is mounted on the end of the bar on a bearing and is a good fit in the spindle. The bearing allows it to rotate with the spindle.

[txcncman]

On most chucks, remove the top jaws. There will be an inner sleeve that helps protect the chuck mechanism help with either 3 or 6 screws. Remove that sleeve and make your adapter from solid to fit. Bore and ID thread your adapter to fit the largest diameter tubing that will slide into the draw tube. Cut and OD thread some tubing to the length needed for your application and make a plug for the stop end. Assemble your stop tube to your adapter and screw into place of the sleeve. Reinstall your chuck jaws.

As Geof is saying, the draw tube moves. This does not mean you cannot use a stop attached to the draw tube, it just means you will lose accuracy. When the chuck jaws close, the draw tube will move a different amount based on material diameter, giving you a different Z position. I have made stops that have an expanding mandrel to grip the inside of the draw tube. Or you can attach a stop to the rear of the draw tube. Anything attached to the draw tube will introduce error into your machining.

The 3 alternatives I mentioned to Geof's idea are the most reliable ways to machine long material lengths accurately (without "eye balling" a line or guessing how much to machine off).

[Anders6612]

If your parts have the same diameter and material, a spindle stop can be used.
The fact that the spindle tube moves when clamping is not a problem.
I have used this method many times, with a reasonable good tolerance.

[txcncman]

If your parts have the same diameter and material, a spindle stop can be used.
The fact that the spindle tube moves when clamping is not a problem.
I have used this method many times, with a reasonable good tolerance.

Be careful. This is also the guy that thinks the metric system of measurement is the only way to go.

[Geof]

The way I see it you have some potential problems using a stop fixed to the drawtube: One is that the drawtube with the stop retracts as the chuck closes so you have to push the part in as it is closing. Or you push the part up to the stop with the chuck open and then hope that it doesn't move while the drawtube retracts as the chuck closes. Either way you sacrifice accuracy.

[txcncman]

The way I see it you have some potential problems using a stop fixed to the drawtube: One is that the drawtube with the stop retracts as the chuck closes so you have to push the part in as it is closing. Or you push the part up to the stop with the chuck open and then hope that it doesn't move while the drawtube retracts as the chuck closes. Either way you sacrifice accuracy.

This is what I was attempting to explain also. Any stop used is best attached to the chuck itself or to the turret.

[haastec]

What about using a spot on the turret face or tooling block?

Jog to a place where the material can touch the turret at a desired length and calibrate your zero to that mark.

[pmurdock]

not sure how that will work.. the one side of the long piece is finished already and inside the chuck bore - the other side would be a rough end (bandsaw finish) how can one accurately use the turret face as a stop on a bandsaw finished end?

[haastec]

not sure how that will work.. the one side of the long piece is finished already and inside the chuck bore - the other side would be a rough end (bandsaw finish) how can one accurately use the turret face as a stop on a bandsaw finished end?

Oh sure! Just call me out on my brain fart!!(chair)

I better have anothe cup of coffee!

Back to the real solutions I guess.

[Anders6612]

Be careful. This is also the guy that thinks the metric system of measurement is the only way to go.

Well, i would really appreciate that you read the whole thread,
not only the topic.