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Member postings for JDEng

Here is a list of all the postings JDEng has made in our forums. Click on a thread name to jump to the thread.

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Thread: Machining what am I doing wrong?
29/05/2011 10:45:28
A lot of the problems with TCT tooling are due to a lack of rigidity in the work or machine set-up and also a lack of speed. If the set up is rigid, then poor finish can often be bettered by increasing the speed and feed - the exact opposite of HSS.
 
I think that there is a tendency to underestimate just how fast TCT needs to be worked to get a good finish, particularly on some of the smaller diameters. Sometimes machines are just not physically capable of going fast enough and it's actually more effective and not much slower to use HSS.
 
I can post some examples of how to work out speed calculations if anyone is interested.
 
John.
Thread: Toolpost Grinding
27/01/2011 11:24:30
There was some debate on this subject on this forum about two months or so ago. Opinion seemed to be divided.
 
When we were apprentices we were always told that the work and the wheel should rotate so that the point where the two met was going in opposite directions. IE. using the above diagram as a guide, for external grinding both should be going clockwise (or anti-clockwise); for internal grinding on the left hand edge of the job, the wheel should go clockwise and the job anti-clockwise.
 
I've never known exactly why but just accepted it however, after the previous debate, I've spoken to a one or two people who have done a lot of universal grinding. The consensus of opinion seemed to be that contra rotation prevents any potential backlash or slackness in drive belts or gears affecting the relative speeds which could mar the finish.
 
John.
 
 
 
Thread: Stuck chuck
05/11/2010 15:01:25
Howard,
 
When you had removed the three capscrews which hold the chuck to the back-plate did you also slacken off and remove the three conical centering screws on the outside diameter of the chuck body? It's a while since I stripped a Grip-Tru but from memory these three screws control the movement of the chuck body on the back-plate and are connected to both.
 
Make sure you mark the back-plate and the body so that they go back in the same relationaship.
 
John.
Thread: Spindle for Raglan lathe
03/11/2010 09:01:22
Ian,
 
Let me say at the outset that I'm not familiar with Raglan lathes however I would make a few suggestions which would probably apply to lathes in general. Some of it might be obvious and if so I apologise for teaching grandmother to suck eggs!
 
1) You say you have clocked (used a DTI) on what I presume is the register for the chuck on the spindle nose and on a centre placed in the morse taper of the spindle. There is a danger of introducing error by clocking on a centre in these circumstances; it would be safer to use the clock directly onto the inside of the morse taper if at all possible. If there is any muck or a bruise between the male and female tapers it will throw the centre out and show up as eccentricity.
 
2) Are both readings of eccentricity in the same place? Mark the spindle nose with a bit of felt tip and make sure.
 
3) Are there any bruises on either register or the inside of the morse taper?
 
4) You say the bearings are "tight". I presume you mean there is no end float along the length of the spindle. Are they bronze bearings or needle rollers/ball races? Are they in good condition? Before you make any decisions I would strip and clean the bearings and make certain that there are no obvious problems with roughness or wear here. Reassemble and try the spindle nose and bore using the clock again.
 
I cannot see any misalignment of the bed affecting the eccentricity of the spindle nose personally; even if it it was so bad that it was putting a twist into the headstock I cannot see how it could make the spindle run eccentric for the type of checks you're undertaking.
 
I undertake machining for a living and agree with what Steve says about cost; it would not be a cheap option to have a new spindle made but it might not amount to that.
 
Just as an afterthought, I appreciate that 0.002" run out seems excessive but are you sure that is was not manufactured that way? As an example I'm in the process of altering an old Zyto lathe bed and cross slide to make a grinding rig for a job and the cross-slide was 0.010" out of square across the bed both vertically and horizontally; there was not a significant amount of wear so it must have been made that way. It's now been corrected but I was amazed that such low standards could have been deemed as acceptable!
 
Sorry if I've waffled but I hope this helps.
 
John.
Thread: Colchester Student owner's question
02/11/2010 18:47:54
Steve,
 
Have you considered telephoning or emailing Colchesters? They are now part of the 600 Group but their technical support department might be able to help. I appreciate that it's an old lathe but they have always been most helpful whenever I've called them.
 
John.
Thread: MEW-169 Tool-post Grinder Article
26/10/2010 08:39:15
Thanks for the welcome Steve!
 
After I had made my post I had a look through various textbooks which I've gathered over the years and they all state that the work and the wheel should be moving in opposite directions at the point of contact but none of them actually give the reason why. Thus they both need to revolve in the same direction if external grinding and in opposite directions if internal grinding.
 
What they do all agree on is that when toolpost grinding you need to achieve the maximum amount of rigidity in the set up if you are to achieve anything like a decent finish.
 
I'm with you Bogs on using a machine; I think you need to take common sense precautions such as covering slideways, cleaning down well after wheel-dressing and at the end of the job etc but at the end of the day they are machine tools for using. I've seen some awful abuse of machinery in industry and it still keeps working - not that I'm condoning that but I do think you've got to keep a balance between practicality and keeping something in cotton wool.
 
By the way has anyone seen the new toolpost grinder by Hemingway Kits?
 
John.
25/10/2010 16:37:12
My first post on this forum!
 
Just to be clear, the job and the grinding wheel have to rotate in the same direction, ie. both clockwise or both anti-clockwise. This means that at the interface between the job and the wheel both surfaces will be moving in opposite directions.
 
From memory, when I was an apprentice (and it is a good few years ago now!!) I seem to remember being told that it was necessary to rotate in this manner because it ensures that the job is ground truly round. If the job and the wheel are moving in the same direction at the interface (ie. one is going clockwise and the other anti-clockwise) there is a chance that, at certain speed combinations, the job will be ground as a series of flats which is clearly undesirable and rather defeats the point!
 
If as Bogstandard is saying, the wheels is losing its edge too quickly then it may be that the grade or type of grit is the wrong choice. If a wheel is working correctly it should expose fresh cutting edges as it works and stay sharp for a reasonable amount of time. It will of course get loaded and dull over time.
 
Regards,
 
John.
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