Member postings for Clive Foster

An effective alternative to old school flat bets is the multi-groove "serpentine" V-belts used for car engine accessory drives et al run Vee side down.

 

Following advice from USA I used one on my Heavy 10 lathe with excellent results although the necessary split and lace up procedure was a pain.  For the Kennedy you only need to find one of a suitable length.

 

Clive 

Generally something to beware of.  The amount depends on the boring bar diameter, shape of the tool tip and depth of cut.  Reason is that during the forward cut there is a force trying to push the bar sideways out of the cut.  Due to the unsupported length and relatively slender nature of a boring bar it almost invariably will be pushed out unless the cut is very shallow.  On the return the bar springs back against the previously cut bore making the unwanted cut.

 

To reduce the effect use the thickest bar you can and withdraw the tool out of cut during the return movement.  When finishing to size take spring cuts at the same feed setting to work out any effects of boring bar deflection.  Normal practice is to accept the effects when rough turning making sure there is enough material left for spring cut(s) when finishing to size. Really its a question of getting to know your tools.  Don't get into the habit of taking teensy weeny cuts.  Job takes forever and by the time you are ready to finish off the tool will be less than sharp so you'll not get a good finish.

 

Clive 

Further to the comment from Jim W

 

Due to the small taper angle MT collets need a lot of drawback to grip.  Taper angle is near enough 50 thou per inch so a 10 thou contraction needs getting on for 1/4" drawback hence the need to keep close to the designated size.  I'm amazed by the + 5 to -10 thou range reported by Ian.  The small taper also means they are very inefficient at gripping things. Much of the draw bar effort goes in overcoming friction as the collet draws back into the socket. 

 

Be worth checking that the bore behind the collet is a bit larger than the standard small end MT 2 diameter of 0.572" so the collet can pull back into it.  Something like 0.59" to 0.6" would be desirable.

 

Clive 

If using a metal roof, especially on a larger shop, put a proper insulated ceiling in and insulate under the roof.  Having a cool attic makes a huge difference to heat transfer rate and stops the damp sweating roof effect.  2" poly board under the metal works fine.  Easiest to do before you put the roof on.  The standard green waterproof chipboad underfloor sheets make excellent internal floors when laid over concrete, well up to machine loads.  Great for bench tops and shelving too being slightly rough so dropped or knocked stuff doesn't skitter over into the hands of the little man who lives under the bench and steals my tools.  Don't use the undyed "just the same stuff".  Surface is loos so its dusty as hell. 

 

Clive 

Many distributor type car ignition systems use a Hall effect sensor with three terminals.  If suitable application info could be found one of these might prove suitable. ( I've got one out of a SAAB 900 squirrelled away in the "mite be handy" box.)

 

Clive 

All this geometrical argument about tool fulcrums and tool lift altering depth of cut is very interesting but it ignores the fundamental causes namely backlash and the forces on the feed screw.

 

 I think everyone agrees that serious parting off trouble begins with the work piece effectively climbing over the tool and trying to draw it deeper into cut.  Whether the climb over effect is due to spindle play, work piece deflection or tool deflection is immaterial as the effect is, for all practical purposes the same.

 

Consider a lathe with the conventional "push from the front" cross slide feed screw.

With a rear mounted tool the screw is pulling the tool into the work.  The screw is in tension, all the play in the bearings and nut mount is pulled out so if the tool is to be pulled deeper into cut by the climb over effect it's necessary to stretch the feed screw.  An unlikely scenario as the feed screw on even the smallest, wimpiest lathe has enormous tensile strength.  Thus the increased depth of cut is generated solely by the climb over effect with no positive feedback to make it larger so there is a good chance of the tool cutting through and the work piece settling back to where it should be.

 

Now with a front mount the feed screw is pushing the tool into the work.  All the backlash and clearances are on the opposite side of the thread and thrust bearings to the working forces.  Being in compression the relatively slender feed screw will try to run away from the load by bowing and shuffling sideways in nut and mounting collar clearances.  A tendency not helped by the offset unbalanced forces inherent to the helical nature of the screw.  Effectively you have a spring, a very stiff spring, pushing the tool into the work.  Now when the work piece does its climb over trick it is able to draw the slide forward through the backlash region and the spring deflection region, the springy bit actually helps the effect along.  The cut depth increases pretty much instantly by getting on for 30 thou or even more on a well worn lathe.  The lathe has no chance of cutting through this, climb over continues until everything comes to a grinding halt with broken tool ruined job and considerable Workshop Esperanto loosely translatable as "oh dear, oh tut-tut, things have gone wrong".

 

It doesn't help the front  mounted tool case that its mounted on the top slide giving an extra set of dovetail slides to reduce rigidity relative to the rear mount case. 

 

Clive 

 

Tom

Sorry I have no more details on the Union machine.  All I know comes from seeing one in a shop, asking what it was and how much then running the tape over to decide that it was too big for my shop.  Double decade (ish) old memory suggests that it was of similar size or a bit bigger than the Astra but a simpler machine with fewer accessories.  Astra is too big for me as well or I'd have sought one out even though a Clarkson needing a very good bath turned up at next to no money.

 

Concerning the down feed problem it might be a good idea to mount a dial gauge so you can see what's going on.  Alternatively we had a piece of scientific equipment at work with an internally geared handle which could be locked up to give a quick movement for preliminary setting then released for fine adjustment.  I imagine that there was some sort of epicyclic gearing inside.  Perhaps there is an affordable supplier of such things.

 

Clive 

Although all traversing table style T&C grinders are, in principle, capable of surface grinding you need to look very carefully at the specific machine in question to decide if it will be able to do a safe, useful, job.  You really have to go and look at the machine. I expect that you have already taken a careful look at things but the way I see it is:-

 

Things to pay attention to are accuracy and quality of the vertical movement, in surface grinding you are dealing with tenths so the method of setting the cut has to be up to this.  In general basic T&C grinders fall down here.  The work envelope tends to be smaller than you'd expect, even worse than small mills in this  respect.  I'd not be surprised to find that the true work envelope of the Chester machine when used as a surface grinder is of the order of 1/4 of the table travels.  As usual the devil is in the engineering details, especially when using for secondary purposes rather than what the machine was designed for.  Table traverse needs to be really smooth, arguably longitudinal traverse by lever is better on a basic & inexpensive machine.  One point I really don't like about the Chester machine as a surface grinder is the direct drive to the grinding wheel.  The wheel needs to stop rather than burst if an excessive feed is inadvertently applied.  With a belt drive system you can easily slacken the belt so that the grinding wheel is lightly driven ensuring that it will stall under excessive feed.  A T&C grinder of this type really needs a more "aggressive" drive which may well be in the danger zone if an error is made.  Lastly the Chester machine is a, relatively, inexpensive device and there is a limit to how much constructional quality can be got for that cost.  Minimum standards for a surface grinder are higher than those for a perfectly adequate T&C grinder.

 

If you need an inexpensive dual purpose machine you may well do better considering machines designed more as basic surface grinders with T&C capability rather than the other way about.  Some of the Union machines for example, however the more advanced T&C capabilities probably won't be possible without a good deal of accessory fabrication.  The Astra AR-5 is impressive if you can find one with all the bits and is very much a dual purpose machine.  Large by T&C grinder standards and somewhat uncommon tho'.

 

Clive 

 

 

RS Components (http://uk.rs-online.com/web/) sell plastic shim stock in individual sizes and assorted sheet packs.  Cuts with scissors.  Colour coded for thickness which is great for sorting out when you get them mixed up.  For example stock no 681-407 is 8 sheets about 6 x 12 inches listed at £12.45 but plus VAT and plus delivery but if you spend more than £25 delivery is free.

Clive 

Clearly this is bad news for users of PowerPC Macs because neither supplier has much incentive to seriously support a now obsolete platform.  I've tried Turbo-CAD a couple of times over the years, starting with the early iteration on an SE30, mainly because the price / feature ratio seemed very good but have always found it less than impressive in practice.  Currently I have, and use, Turbo-CAD MAC and MAC Pro on my G4 Dual 1.25 GHz desktop with OK results but there are many areas that I don't really like.  Formatting in particular is totally counter-intuitive and its habit of re-dimensioning drawings to suit what the current preferences are when you open them can be "foot through the screen" frustrating.

I bought VectorWorks Mechanical 10 on redundancy a few years back, exploiting the computing equipment for new business help then available, but never really got going with it.  Upgrading is very expensive and help, in the UK poor.

Fact is for a casual user seeking a pencil and drawing board replacement Claris-Draw / Mac-Draw Pro remains a pretty much unbeatable combination for ease of use and just enough features.  Pity its two processors out of date.  Easy-Draw bills itself as the modern replacement.  In a way it is but the file sizes are huge and its dog slow being just about fast enough to use on my system.  In comparison Mac-Draw Pro flies on an SE30 nominally 50 times slower.  A major reason why I've never really got into mainstream CAD is that 20 + years of experience with Claris and Mac Draw meant that I could make it do pretty much everything I need.

Clive