Here is a list of all the postings Alan Jackson has made in our forums. Click on a thread name to jump to the thread.
|Thread: Vertical Parting Tool|
Andy & David I do agree with what you say but a vertical parting tool seems to be an approach not tried. Because it avoids the rotating forces applied to the topslide and cross slide whether the cutting tool is mounted on the front or rear of the lathe. I suggesthese rotating forces create movements at the cutting tool which can create chatter and dig ins etc. Even with well fitted slides etc when a parting tool digs in it is suprising how much movement is instantly created. So that is my reasoning/justification/food for thought.
SteveW, I have added a couple of pics in my album I don't know how to do it here in this message hope they are more illustrative
Andy1 & David littlewood, Thanks for your interest and you certainly have not rained on my parade. My reasoning for a vertical cutting tool is that in both cases front or rear mounted parting tools, the cutting tool is subjected mainly to bending stresses. The greater the cutting depth the bigger the cantilever and the greater the bending moment. In essence the extended cutting tool is just like a ruler in classroom; where kids love to hold it extended over their desk edge and flick it so that it viabrates. By mounting the cutting tool vertically it is supported from below and the cutting forces are mostly directly downwards putting the cutting tool in compression rather than bending, because the cutting edge is directly supported below with no cantilever. I suggest that this avoids resonance due to a cantilevered support and avoids the stress concentration where the cutting tool meets it support block. It also allows the cut swarf to freely exit over the top of the tool. All these advantages allow the cutting edge to be thinner which also reduces the cutting forces. The downside is that you have to have a lathe that can safely rotate the mandrel clockwise without the chuck unscrewing, so threaded mandrel noses are no good for this. Parting off has always been a problem with model engineer size lathes which has been helped by the greenwood tool mentioned but the geometry still exists.
Edited By Alan Jackson on 23/04/2012 15:59:41
Yes John it is cutting mild steel
I have just made a vertical parting tool for my Stepperhead lathe. I first tried a normal parting tool mounted vertically but it suffered from scuffing on the parallel sides of the tool which is at the last part of contact with the metal being cut. So I made a one piece tool by silver soldering a small part of a high speed steel parting tool to a slightly thinner sheet of steel. Then I ground the high speed part to have clearance in both directions and it worked very well. It is nice and rigid in the cutting directions, with no bending for the parting tool. The mandrel rotates in a clockwise direction for a rear tool post which will be a problem for lathes with screwed on chucks so they would have to have the tool mounted at the front of the lathe. Here is a short video of it operating. It is only cutting off a 20mm dia. because I could not hold the camera and apply cutting oil with a brush at the same time but I will try it with larger diameters. But so far so good. Why has this not been tried before?
|Thread: MEW 186 - Electronic Lathe Control|
On my Stepperhead lathe I use TurboCNC with one pulse per rev, this is a basic DOS program. It can cut G33 and G76 screw cutting modes very well. It is better to choose the low belt drive mode (Back gear mode) to ensure speed stability and adequate torque availability as this ensures an accurate thread pitch. I can also use it in a half CNC manner by setting G33 in MDI mode (Manual Data Imput) for screw cutting and using the retractable top slide set at 27 or 30 degrees and use the top slide to set the cut depth, manually retract the tool then change the G33 Z parameter to plus from minus ( or vice versa) to return the threading tool back for the start of a new cut, return the topslide back to its previous position, add a new depth of cut, reset the G33 Z parameter back to its previous setting and start the new cut by pressing the return button on the computer, and do this as many times as is required to complete the screw thread. While this may sound long winded it is actually a quick and simple process when observed. with no watching the thread dial as on a manual lathe to feed in the tool at the right moment. The big advantage is that there is no set up required to ensure the thread is cut to the required depth before starting the process, which suits one off operations.
Edited By Alan Jackson on 22/01/2012 12:39:24
Edited By Alan Jackson on 22/01/2012 12:49:27
Edited By Alan Jackson on 22/01/2012 12:51:29
Edited By Alan Jackson on 22/01/2012 12:53:31
Edited By Alan Jackson on 22/01/2012 12:56:00
|Thread: This is a test thread to check postings|
|How is it that Homeshopmachinist and Homeworkshop.org get by without so many flashing ads?|
Thank you Paul, now all flashing ads gone
|Thread: The perfect ME Lathe|
I proposed and built a design for an ideal Model makers lathe in MEW151,152&153. This seems to incorporate many ideas suggested in this thread. It also has a top slide that can be positioned anywhere on the cross slide, which was described in detail in MEW 119,120 & 121. It was mistakenly referred to as a CNC lathe but is much more than that as it can work equally as well in manual, powered driven axes or full CNC axes. The idea is that the operator can choose (and even mix ) these operations together to get a range of versatility which is not possible with existing available machines.See thishttp://www.lathes.co.uk/stepperhead/
Edited By Alan Jackson on 28/09/2011 11:56:49
Edited By Alan Jackson on 28/09/2011 12:04:53
|Thread: MEW 180|
If it is offered as a concept, it is therefore put up as an untried design for review.The premise of the design is to save the forces being applied by the existing saddle drive mechanism which is not designed for the proposed axial shaping forces, it applies the force at the lowest point of the saddle. This leaves the cross slide and topslide to deal with the bending moment due to the distance up to the centre height. Putting bending forces onto the topslide, which also is not designed for this. A design which applied the axial force higher up and in line to the cutting tool direction would avoid the bending moment being applied to the topslide and cross slide. As such the design only achieves about half of its premise that it proposes to protect the lathe from axiaI shaping forces that it is not designed for. Is this fair criticism?
Figure 9 on page 40 of MEW180 shows a right angled slit into the bore to clamp the shaft.
This is a good example of computer design which is untested. How would you propose a potential builder would cut this slit? If we all can do proposed designs in virtual reality using virtual materials which are strong, hard, straight and cost free it will save a lot of trouble doing things the old fashioned way. If this had happened a few years earlier I think Myfords would have closed down much sooner than they did. Also just think of the electricity saved by going virtual, the new green model engineering.
|Thread: Parting off on Myford lathes|
I generally agree with TerryG' s summation that a rear parting tool post works best. I have spent many hours being petrified at parting off on lightly constructed lathes with average head bearings etc. Now the rear toolpost on my chipmaster works easily without fear. I have also experimented with front and rear cutting tools and reverse rotation upside down mounted tools and believe that rear inverted cutting position works best on light lathes because the cutting tool does not seem to get to the dig in position so easily, it becomes less resonant. The cutting forces seem to reach a more stable situation and this shows up in a better finish.
Edited By Alan Jackson on 19/01/2011 17:44:19
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.