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Shims for packing up cutting tools

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thomas oliver 201/08/2014 18:48:38
104 forum posts

I have a compartment box in which to keep shim. I measure and mark all the strips with their thickness, When shimming a tool I stick the shim to the bottom of the tool with double sided sticky tape. On my Boxford, I made tool holders for small 3/16th square HSS bits with the tool slot at a small upward angle. The tool was fixed with short Allen grubscrews, set to centre height, then clamped in the normal way. Both methods allow instant tool clamping. LIke John Macnamara, I find that a four way tool post and HSS tools perfectly adequate for all of my work which includes model diesel engines, steam engines and locos, vintage motor-cycles and so on. It must be realised by beginers to modelling that most model parts require sharp shoulders to allow close fitting. TC tools have slightly rounded noses and I find them useless for most of my work and much prefer HSS which is easy to grind. I use TC tools for Cast Iron and tough steels when necessary.. Why go to the bother of buying expensive tangential tooling or having the tedium of making them in profusion when the old 4-way does the job adequately. Can a normal lathe tool be ground to the same angles and produce the same results as a tangential tool? I have not tried. Maybe someone has and can enlarge on it.

Jon Gibbs01/08/2014 19:11:00
738 forum posts

I like the idea of the double-sided tape but cheap feeler gauges and odd bits of flat stock for thicker shims are my parts of choice.

**LINK**

At £2.60 a pop and guaranteed burr-free flatness it seems a steal to me - HTH.

My biggest problem with my 4-way is that every side is a different height!

Have taken the plunge to a Dickson QCTP though. Can't wait to try it out.

Jon

frank brown01/08/2014 19:42:10
436 forum posts
5 photos

I too have a shim box (or two), the problem is that 16 SWG shim is too thick and the next i can find is .8 MM, or a variation of the above. I seem to spend too much time shuffling through the boxes, micing up bits (writing the value on them) and only to come to some conclusion like I'll change the .25" block for a 4mm and start again.

Soon I shall make a selection of shims based on some thing I can mill, taking as an example, gauge block sets, So I shall get a piece of 1/8" /3mm steel cut a couple of shims of the end, then mill off .005" all over and then cut two more shims, then cut another .005" off and repeat, so I'll have a series of gauges based on 0, -5, -10, -15, -20, -25, -30 thou. So that's seven milling operations, a posher way is to have a 1, 2, 4, 8, 16, 32 progression, that would give a 0 -> 63 range with seven shots on the milling machine and a stack height of 0 to eight times the thickness of the material used. I'll have to check and see what the typical shim size is.

The height of the cutting edge must never be above the centre line, else the front edge of the tool is rubbing not cutting, however having the tool too low just reduces the amount of top rake. So this is directly scaled from the diameter of the work. So I reckon TAN 1 degree is .0174, that means if you are turning a bar of 2" diam, if your tool is .017" below centre,its effective top rake is reduced by one degree. OK for Ali (starts off at six degrees), bad for brass tool starts of at zero degree. Like wise extremely poor for turning .01 diam watch spindles

Frank

Edited By frank brown on 01/08/2014 19:44:27

John Durrant01/08/2014 21:38:44
44 forum posts
4 photos

I have spent most of my working life shimming tools in a four way tool post. I am now retired and will spend the next few days making Howard Halls QTP for my hobby lathe. I will then have a shim bin.

Bazyle01/08/2014 23:39:39
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5006 forum posts
198 photos
Posted by frank brown on 01/08/2014 19:42:10:

The height of the cutting edge must never be above the centre line,

The Boxford (originally South Bend) book "Know your lathe" actually recommends setting it above centre with good reason. Not applicable to watchmakeing perhaps but by setting it high it produces a component of force outwards or back along the tool that keeps the cross slide nut play taken up.

frank brown02/08/2014 06:59:35
436 forum posts
5 photos

I think that last statement needs a bit of clarification. Its top of page 20 and applies to an angled tool holder where the tool is pointing upwards by 20 degrees or so. The tool also needs more front clearance. This type of tool holder has the advantage that as the tool is re-ground, it can be slid forward before clamping in the holder to keep the cutting edge at the correct height - even if it is for only one diameter.

Beneath that bit is a long list of where the tool must be set at center height, so the above centre setting is less then versatile.

I think that there is a lot of mileage in those angled tool holders, because the amount of work to make them looks a lot less then with a "quick change tool holder", so they should be cheaper. The cutting edge can be reset to the correct height after tool re-sharpening. The only odd thing is that the tool AND holder must be used when sharpening tools so the angle of the holder can be compensated for. They are clearly impractical for things like boring bars. Very suitable for parting tools, if the angle of slope is the same as the top rake required (as G H Thomas designed?).

Frank

Neil Wyatt02/08/2014 10:48:03
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17375 forum posts
690 photos
77 articles

A tangential tool holder and a quick change toolpost aren't mutually exclusive.

Neil

tangential qctp holder.jpg

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