Lathe Cross Slide Problem

[f350ca]

Just curious, but you jumped from remounting the nut that you thought was the problem to making a new lead screw and nut. The machine seams fairly new, so one section of the lead screw should not be wore more than the rest. Is the axial play in the nut on the screw equal to the movement you were seeing on the cross slide? Fixing the mount and splitting the nut to remove backlash would seam like an easier fix.
Making new parts is fun but may not cure the problem.

[EdK]

(04-24-2014, 05:12 PM)f350ca Wrote: Just curious, but you jumped from remounting the nut that you thought was the problem to making a new lead screw and nut. The machine seams fairly new, so one section of the lead screw should not be wore more than the rest. Is the axial play in the nut on the screw equal to the movement you were seeing on the cross slide? Fixing the mount and splitting the nut to remove backlash would seam like an easier fix.
Making new parts is fun but may not cure the problem.

I don't believe it's a backlash issue. The nut I have has a split in it already to remove backlash. I think it's probably a combination of poor mounting and poor design of the nut. I'm not making the new lead screw and nut. Ken offered to make a properly designed nut and lead screw so I accepted his offer. At least I'll know I'm working with good parts when I get the new parts.

The movement I was seeing is much more than the backlash I have.

Ed

[DaveH]

(04-24-2014, 06:02 AM)EdK Wrote: The only critical length dimensions of the whole lead screw are the ones starting at the shoulder to the left of the hole for the spring pin and going right to the end of the lead screw. That total distance sets the location of the feed gear.
Ed

Hi Ed,
In that case it would be best to dimension that way.
Just saying

DaveH

[EdK]

The only thing I got done this evening, besides updating the drawing, was to get that knurled bushing knocked out. It was somewhat of a bear to remove without a proper press (yet another project that needs finishing).

Ed

   

[stevec]

(04-24-2014, 11:54 AM)EdK Wrote: As is usual with these import lathes, the hole in the gear is not through the center.

Exactly why I offered my suggestion.

[EdK]

(04-24-2014, 06:08 PM)DaveH Wrote:

(04-24-2014, 06:02 AM)EdK Wrote: The only critical length dimensions of the whole lead screw are the ones starting at the shoulder to the left of the hole for the spring pin and going right to the end of the lead screw. That total distance sets the location of the feed gear.
Ed

Hi Ed,
In that case it would be best to dimension that way.
Just saying

DaveH

Dave,

I have dimensions in those places so I'm not following you.
So please don't "just say" but provide some useful information. Most of us are not drafters or machinists by trade so it would be more useful if you provided clear information rather than cryptic remarks. Most of us are here to learn, at least I am, but I can't learn anything from comments that don't provide any information. I'm assuming I didn't dimension it properly so tell me how I should have done it.

Ed

[EdK]

(04-24-2014, 07:39 PM)stevec Wrote:

(04-24-2014, 11:54 AM)EdK Wrote: As is usual with these import lathes, the hole in the gear is not through the center.

Exactly why I offered my suggestion.

Steve,

I went back and reread your post and I guess I should have mentioned that there isn't enough meat on the gear to guide a drill bit. Only .080" thick which isn't enough for me to rely on for guiding a drill bit. That's why I am going to rotate it 90 degrees on the lead screw and drill a new hole.

Ed

[DaveH]

The main aspects of dimensioning is so the machinist can make it as the designer/draughtsperson wants or needs it.
Dimensions are usually taken from a datum, there can be more than one datums.
The linear dimensions are best dimensioned from a datum (or two).
It is usual to give an overall length.
There has to be some "give" in the dimensioning of the part ie. some lengths are left dimensionless.
Eg. on your drawing the first 3 dimensions on the right add up to 1.00 + .48 + 4.08 = 5.56. Now is that the distance you require the step to be from the right hand face? What happens when the machinist makes it (bearing in mind it is difficult to make anything exactly) and the 1.00 length comes out to 1.010 is this dimension OK? Now does the machinist make the next step .48 or do they take off the .010 and make it .470? Lets say it is made .49.
Should the 4.08 length be made to take into account the actual lengths of the previous steps made? If it happens to come out 4.08 we have 1.010+.49+ 4.08 = 5.58.
(Remember it is difficult to get each and every length exactly right)
Initially from the drawing the length to the .625 dia step is 5.56" and the machinist made it 5.58" Does it matter? If that length (5.56") is important then the right hand face is used as a datum and the dimension of 5.56 is placed from the datum to the .625 step. One of the three dimensions 1.00; .48; 4.08 is then omitted usually the least critical.
The dimensions are the most important part of the drawing - it tells the machinist which part(s) are important so it can be made that way. The machinist also needs some leeway to make the part.

Now if you are the machinist/designer/draughtsperson you will know which are the important dimensions and which are not so important so how it is dimensioned for you doesn't matter.

I have said it before the dimensioning of a part is the most difficult aspect of the drawing, but it is up to the designer/draughtsperson to dimension it in such a way that the machinist can make the part exactly the way that is wanted/needed.

There clear as mud

DaveH

[EdK]

Dave,

Now we're getting somewhere.

I think I understand what you're saying and it makes sense so I'll take a stab at updating the drawing so it can be critiqued for better clarity.

Ed

[stevec]

(04-25-2014, 05:54 AM)EdK Wrote: Steve,

I went back and reread your post and I guess I should have mentioned that there isn't enough meat on the gear to guide a drill bit. Only .080" thick which isn't enough for me to rely on for guiding a drill bit. That's why I am going to rotate it 90 degrees on the lead screw and drill a new hole.

Ed

Ed, maybe I should have said position the drill instead of "guide" it so as to start it in the same spot as the hole on the original.
However, you did mention that the gear was a loose fit originally so if you're going for a loose fit on the new leadscrew just disregard my ramblings.