Author Topic: Boxford CUD poor cutting  (Read 4168 times)

Offline diagnosticated

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Boxford CUD poor cutting
« on: July 13, 2016, 06:07:11 AM »
Hi Guys.  Having watched that man on youtube, I bought an ex education boxford cud lathe from the usual source as a hobby lathe. My problem is this: Facing cuts are lovely and smooth but longitudinal cuts are terrible. The finish looks like a screw thread.  The cross slide seemed to have far too much play so I replaced the thrust bearings. Play reduced slightly but finish was still rubbish.  I made a spacer/washer to take up 90% of the play in the cross slide but longitudinal cuts are still poor.  Any ideas??  I cannot feel any play at all in the headstock.  I have the boxford cutting guide book with set up instructions but as I cannot make a smooth turn on a bar it is hard to follow the set up instructions. Is it possible for the headstock to be out of alignment with the bed?  Grateful for any help as lathe is no good like this despite looking in good condition. 

Offline Joules

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Re: Boxford CUD poor cutting
« Reply #1 on: July 13, 2016, 06:56:08 AM »
 :worthless:

You need to show us your problems.  Oh and welcome to Madmodders
Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Offline DavidA

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Re: Boxford CUD poor cutting
« Reply #2 on: July 13, 2016, 07:43:06 AM »
Try a cut with the gib strips tightened up until you can hardly move the cross slide and top slide.

Also maybe use a clock guage to check around for wear.

Dave.

Offline mattinker

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Re: Boxford CUD poor cutting
« Reply #3 on: July 13, 2016, 08:19:45 AM »
If you can face off cleanly, I don't think there can be much wrong. To encourage you, it sound more like operator than machine oriented. Some photos or even a video would be a good idea!

Welcome aboard, regards, Matthew

Offline Will_D

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Re: Boxford CUD poor cutting
« Reply #4 on: July 13, 2016, 08:28:16 AM »
Hi and Welcome.

I agrree with Matt, if you can face off then the crossslide is fine. It sounds like play in the saddle or top slide.

If you can get hold of a clock gauge or even just the end of a tool and feeler gauges try this.

Piece of 1" bar about 12 " long chucked in 3 jaw. Lock the headstock so chuck can't rotate.

Set the tool or clock gauge to overhang the cross slide ( say a 2" cut with the top slide )

Set the tool or gauge to touch in the middle of the 12" test bar.

Now grab the top slide and wiggle and waggle to show up all the plays in the 3 gibs!

Adjust as required

HTH Will
Engineer and Chemist to the NHC.ie
http://www.nationalhomebrewclub.ie/forum/

Offline chipenter

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Re: Boxford CUD poor cutting
« Reply #5 on: July 13, 2016, 03:06:40 PM »
Sounds like the problem is the saddle any dings on the bed or ware and it caan rock , http://www.pulse-jets.com/boxford/boxford_know_your_lathe.pdf another on to look out for is Southbends how to run a lathe , Boxford is a copy of the Southbend 9" lathe .
Jeff

Offline RussellT

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Re: Boxford CUD poor cutting
« Reply #6 on: July 13, 2016, 05:03:13 PM »
Start with the simple stuff first.  Tool angles are crucial, chucking is important.

How much do you have sticking out of the chuck?  Is it the same bit you faced?  Is the material the same?

If you can face stuff OK I don't think there'll be much wrong with the lathe.

Russell

Offline diagnosticated

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Re: Boxford CUD poor cutting
« Reply #7 on: July 15, 2016, 02:38:19 AM »
Thanks for welcome and suggestions guys.  I will try to take some dti measurements.  I was just confused because of the free play in the cross slide that I have removed with a washer.  Is it normal for the cross slide to have nothing to take up play?  I have the boxford parts diagrams and they do not show anything other than the two thrust bearings. (although the pictures are poor)

DTI measurements: 1" dia bar 8" long.
Run out at 1/2" from chuck. 0.002"
Run out at  5" from this point. 0.008"
With the dti set to zero when I move saddle to the 5" point the dti shows a deviation of 0.002"

I was not sure about the bar so I swapped to a known parallel and repeated above at 1/2" from chuck and 2. 1/2" from that point.
Run out at 1/2" from chuck still 0.002"
run out at 2. 1/2" from this point. still 0.002"
With the dti set to zero when I move saddle to the 2. 1/2" point the dti shows a deviation of 0.001"

So my results suggest a run out of 0.002" at least over the first 2 - 3" from the chuck.  Is this good enough?
The results also suggest an out of parallel of 0.001" over approximately 2. 1/2" Is this ok?


« Last Edit: July 15, 2016, 05:43:13 AM by diagnosticated »

Offline RussellT

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Re: Boxford CUD poor cutting
« Reply #8 on: July 15, 2016, 05:37:39 AM »
Yes it's quite normal for there be nothing to take up play.

However there are two sources of play.  One is the backlash between the cross slide screw and nut - there's not much you can do about that.  Even new screws and nuts won't reduce it to zero.  Some more expensive lathes have nuts that you can adjust to reduce the backlash.

The other source is the clearance in the bearing on the cross slide screw.  You can adjust that to a minimum, the handle is screwed on to the end of the screw with a lock nut and a grub screw to lock it in place so you can adjust that.

None of this should prevent accurate work as each time you advance the slide you are pushing it into the work and you have taken up all the clearances.  If the material and tool geometry combine to pull the tool into the work that may cause a problem - you can solve that to some extent by altering the tool geometry and making sure the gib screws are snug.  If all else fails you use a gib screw to lock the slide during a longitudinal cut.

Russell

Offline diagnosticated

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Re: Boxford CUD poor cutting
« Reply #9 on: July 15, 2016, 05:52:14 AM »
Thank you for helpful reply Russell. The free play was not backlash as such. I have very little backlash.  The free play was literally two much spare space on the fixed end of the screw.  I could not take it up with the handle because the handle was in its factory set position which was already in as far as it can go.  That is what seemed odd. I replaced the thrust bearings thinking that these must have worn but with new bearings the clearance was almost the same. That is why I have now added a shim washer. The clearance is more or less zero now but I still have backlash between screw and nut which I expect.  The tool post fitted is mounted on ball bearings. It only allows the cutting tool to sit at 90 or 45 degrees to the center line.  Could this be a problem with index tooling?

Offline jiihoo

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Re: Boxford CUD poor cutting
« Reply #10 on: July 15, 2016, 10:32:17 AM »
Hi,

As the backlash & free play don't seem to be the issue, it is time to get back to the basics for a while. I started thinking what could cause longitudinal cuts to be bad but not affect facing cuts. Both of these suggestions are really "back to the basics"; I am asking them since we don't know your background and it is possible that you have overlooked these. Please don't be offended if these are already crystal clear to you :-)

1)
Is your cutting tool set at exactly center height? If the tip of your cutting tool is below or above center height, your facing cut could still be ok but the longitudinal cut would not.

Put a dead center on the headstock (or tailstock, assuming your tailstock is properly at the same height as your headstock; it should be...) and compare the height of the point of the dead center to the tip of the cutting tool. Are you below or above?

Or you can test it like this (assuming your tool height doesn't change when you change between facing and turning): make another facing cut. When you are done, is there a small nib or pip left at the center of the part? If you see a nib, you are below centerline. If you don't see a nib, you could be above centerline. Adjust the cutting tool down and make another facing cut; repeat this cycle until the nib appears and then go up just enough to get rid of it (or until the nib that is left is so small that you can pry it off with your fingernail).

Here is one way to check the center height of the cutting tool: http://www.instructables.com/id/Correct-Lathe-Cutter-Setup/ (Click on the "View all steps" button).

2)
How are you feeding the tool when turning? Are you feeding it manually or using a power feed? If manually, have you noticed that the "gearing" of the handwheel on the saddle is way faster than on the crosslide handwheel and you should turn the wheel much slower. If using a power feed, what is your step per revolution (0.1-0.2mm / rev aka 0.005-0.01" / rev is in the ballpark). If you are feeding too fast compared to the speed at which the part is turning, you will get the screw thread effect.

If neither of these was it, then I think some pictures would be good. At least a pic of the finish that you get when turning would be needed. Seeing what kind of screw thread effect you are getting will probably be the key. A pic showing the cutting tool near the turning part might also be helpful.

Cheers,

Jari

Offline RussellT

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Re: Boxford CUD poor cutting
« Reply #11 on: July 15, 2016, 12:44:22 PM »
The tool post fitted is mounted on ball bearings. It only allows the cutting tool to sit at 90 or 45 degrees to the center line.  Could this be a problem with index tooling?

I have a Boxford 4 way tool post which indexes at 45 degrees.  A previous owner removed the indexing mechanism as it is no help.

Some times you will need to loosen the tool post and rotate it to present the tool to the work at the correct angle.  That will only be a problem with indexable tooling if you need to move the toolpost in between tools that you wanted to replace exactly.

Russell

Offline diagnosticated

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Re: Boxford CUD poor cutting
« Reply #12 on: July 17, 2016, 10:03:34 AM »
Thanks guys.  I got a result. It is the 4 way multilok HFC (turrets) ltd tool post causing my problem.  The tools post is flexing which is something I have not seen before.
I took out the bearings and added shims so it rotates and locks in any position (rather than 45 degree steps) and the cut is now ok.   The tool post looks so substantial I never considered that it might be moving.  I really appreciate the help guys.