Member postings for ega

I used Hammerite Special Metals Primer available from Halfords and no doubt elsewhere on the aluminium castings of my Speedy recumbent trike. You can overpaint with "most paints" and clean brushes with water. My topcoat is still there.

Andrew Johnston:

garrygun said "affordable". I imagine you know more about this than I do so what would you suggest?

Incidentally, in my post what was intended to be a right bracket has come out as an emoticon.

My vintage Willson slantbed came with a Burnerd Multisize collet chuck and collets designated MC3 -13 (1.125" - 1.5". These look similar to the EC collets mentioned by KWIL and I was interested to see from the Rotagrip website that EC collets can be used with hexagonal as well as smooth round stock. If you have the money you can also get collets with serrated jaws for gripping black bar, etc.

Depending upon what is meant by "affordable", I would consider a taper-mounted ER40 chuck and collets (range 3-26mm).

Ian S C:

Sorry if I wasn't clear - I did find your table in your photo album. I see you have now been able to transfer the photo to this thread, something I have yet to attempt.

I did, however, produce a thread in softish aluminium without difficulty. As it happens, my Roltap brand tool turned out to be marked with a tap drill size - 7.4mm - and I actually used 7.35 which was my nearest drill and fell neatly between the high and low range figures. Under a lens the thread appeared to be not quite fully formed.

Harold Hall makes some interesting comments including that a good quality lubricant, not a cutting oil, must be used; my favourite Rocol RTD claims to be suitable for "forming operations"

PS

I realize I have committed the all-too-common sin of asking for information which I should perhaps have first looked up myself. The up side is that the many see potentially useful material rather than just the one.

I looked out my single 5/16" 24 UNF thread-forming tap and ran all three methods of determining the correct tap drill size with results varying between 7.3mm and 7.4mm. This might seem quite a large range but there is the variable of thread depth to consider; I used 75% for the Guhring calculator.

I also checked three other possible hardcopy sources:

Machinery's Handbook 1943 - apparently unknown then

Newnes Mechanical Engineer's Pocket Book 1997 - not mentioned

Tubal Cain's Handbook - not mentioned so far as I could see but he was very keen on the correct size for conventional taps

Harold Hall's Data Book (WPS 42) - he calls them fluteless and gives 7.3mm

Now off to the workshop to form a thread with the thought in mind that these taps presumably require a relatively large degree of axial pressure.

Many thanks to Versaboss, Andrew Johnston and Ian S C for their information.

Prompted by the original post I searched the forum for "TiN coating" and was surprised to get no results. What do the knowledgeable say about this modern fashion?

Andrew Johnston: I have one of these thread-forming taps and read your comments with interest; does any one publish tables of recommended tapping sizes for these or do you just go on progressively reducing the hole size until a full form thread is achieved (and then stop!)?

Stub Mandrel:

Thank you - that seems very clear. The tip of a push rod would seem to be an ideal application but when a larger surface is involved only the last part treated seems likely to be hot enough to gain from the quenching. I shall therefore re-heat all over before quenching in future.

colin hawes

Thanks for the further information.

colin hawes:

Thanks for your post. What intrigued me about this method was that I had always understood that case hardening was a two-stage process - first introduce the carbon under heat then quench to complete. I seemed to get some kind of effect without quenching. Tubal Cain (WPS1) is very good on this subject and makes a good argument for choosing case hardening mild steel over through hardening silver steel, etc.

Russell Eberhardt:

I agree that hard on hard seems wrong and, in any event, suspect you know more about this than I. However, one authority (the late Cliff Bower) said "clamping screws for tool-posts should always be made of high-tensile and case hardened material and the lower ends bevelled neatly". He went on to suggest drilling the ends and inserting a standard (presumably, hardened) steel ball-bearing making the interesting point that screws treated in this way do not tend to shift the toolshank when tightened.

I personally use standard HT capscrews treated as you suggest and try to avoid overtightening.

My Oxford arc welder has a 12V tapping which can be used with a carbon rod in the electrode holder to heat and solder, etc. The brief instructions also claim that the carbon can be used to harden steel. I had never tried this until very recently when I found that it seemed to work after a fashion.

Has anyone any experience of this method or helpful comment to make?

Someone experiencing parting off problems would do well to start by reading the relevant passage in George H Thomas's book. My own experience improved radically when I built his rear toolpost some years ago. More recently, I invested in a Greenwood KIT-Q-CUT and had very good results using it in a custom turret on the GHT toolpost on a Super Seven.

The Greenwood tool is based on a Sandvik p/o blade and insert and appears to be half a standard double-ended blade fastened by two countersunk screws to a rectangular block intended to be gripped in a clamp type toolpost. This design works but is not as robust as the standard Sandvik arrangement, the shear strength of the screws being the limiting factor. At some stage I added a third screw and later still three dowels. The beefed up tool also worked very well in the standard toolpost on my larger lathe until I had a major seizure and succeeded in breaking both tip and blade (I will aim to post a photo of the result).

This happened shortly after I had bought two replacement tips including one of the new ones with an angle to reduce the pip. When I learned that the standard, double-ended Sandvik blade, costs about £70, I decided to try the Front or Rear tool advertised on this site and find it excellent. If anyone wants to take the two Sandvik inserts off my hands at cost less 10% they are welcome to message me. There are cheaper versions eg the Glanze but this is not as effective as the Sandvik in my experience.

Happy parting!

I have now posted photos of the components of my gauge and of its use for setting the Myford topslide.

By way of additional explanation, "R" on the gauge label is the distance between centres of the two 12mm dia columns; these project below the base plate sufficiently to engage the c 8mm dia rod when it is located in the dovetail of the topslide (it is, of course, necessary to remove the top of the slide to make the setting).

"N" is the wall thickness of the setting ring derived by trig as indicated on the label.

The gauge is held on the topslide base by the clamp on the other side from the rod. Removing and replacing the top of the slide is made easier if one has dowelled the gib as recommended by GHT. I believe that late model Myfords have a flat-topped slide and it may then be possible to operate the gauge from the flat top provided that the geometry is correct; it is necessary to align the gauge with the slide travel.

In the photo the setting is being made to a test bar held in the tailstock. The bar could perhaps better be placed in the spindle taper. For convenience, Peter Smith's original suggestion was to align the gauge to the extended tailstock barrel but on the Myford this would mean a limited "R" distance. The 8 deg setting ring is shown supported by friction only but in practice it may be more convenient to provide packing so that it sits at the appropriate height and to verify the setting position by trapping slips of cigarette paper between gauge and test bar.

I hope this is clear and that it helps someone other than me - if so, give thanks to Peter Smith.

Some further interesting postings.

Douglas Johnston: so far as I can see I can only upload JPGs to an album. For the moment, therefore, I have uploaded only the JPGs in Smith's description. Beyond these, as well as explanatory text, there are a number of GIFs; I will give some thought as to how to make these available and also photograph my own version and post in due course.

If the aim is 8 deg, as opposed to matching an existing taper, then P J Smith's Taper Turning Gauge is well worth considering. It works on the sine bar principle, is straightforward to make and has the great practical advantage of positively aligning the topslide before it is tightened. Unfortunately, the web page describing his device seems now to be "unavailable" but I have the relevant files on disk and no doubt there is some way they could be posted to this site together with a photo of my own version if these are of interest.

The gauge works equally well for larger and smaller angles so would come in for morse tapers and 40 deg included angle collets as well as the ER variety. Finally, it provides an opportunity to brush up one's trig!

I note from one of the helpful threads here on ER collets that John Stevenson found it necessary to correct the nose of his collet holder by grinding it in situ and would be interested to know if he has written up the process anywhere. I imagine that most of those who make their own holders turn the taper but, of course, the commercial item is ground (and, presumably, hardened).