DIAMOND TOOL HOLDER
Road tested by Roger Bunce

Summary

Eccentric Engineering's redesigned RH Diamond Tool performs very well on a wide range of commonly used model engineering materials. The tool is far easier to sharpen than a conventional tool and the optimum cutting angles are set automatically. For this reason the Diamond Tool is also considered safer to sharpen than a conventional tool. Furthermore, it is easier to set up, and does not require packing to set the tool on centre. Hence, the tool is ideal for newcomers to lathe work as well as experienced turners.

In conclusion, the author considers the Diamond Tool an excellent product and now uses it in preference to a conventional tool. It should rank high on the model engineer's wish list.


Introduction

The Diamond Lathe Tool Holder, made by Eccentric Engineering, Melbourne Australia, belongs to the category of cutting tools that act tangentially, rather than radially to the diameter being turned.  The concept is not entirely new; machine tool makers such as Alfred Herbert and H. W. Ward were using tangential tools in the early part of the last century. The main advantage of tangential tools is that they are much easier to sharpen than radial tools and retain a constant cutting form. It is surprising, therefore, that they have not superseded conventional types. It may simply be that, as far as small lathes are concerned, tangential tool holders have not been commercially available – until the advent of the Diamond Tool Holder.


Description

Photo 1 shows the redesigned RH Diamond Tool Holder fitted with the standard combined surfacing and facing tool bit (LH tools are also available). The tool holder comes in 8, 9.5 and 12mm sizes. The tool shown is the 12mm and this is fitted with a ¼" HSS tool bit.
Very briefly: The tool holder is made from high quality, heat treated, 4140 steel castings, and all functional surfaces are machined. The tool bit is set tangentially to the diameter of the work piece, tilted to give front and side clearances, and held in place with a single fixing screw. The tool is sharpened by grinding just the 'top' of the tool bit to form a diamond shape, using the simple grinding jig supplied (Photo 2). The tool bit can also be sharpened for screw cutting using the same grinding jig. For more information on the Diamond Tool Holder, including selecting the correct size for a particular lathe, and a video of the tool in action see: http://www.eccentricengineering.com.au/


The redesigned Diamond Tool Holder differs from the original design in the following way: The crank angle is more acute so that, with the body of the tool set at 90 degrees to the turning axis, the cutting clearances allow surfacing and facing at one setting. A further advantage is that, when using the LH version of the tool for screw cutting, there is more clearance between the body of the tool and the chuck.



Testing

The tests were not intended to be comprehensive; this was because of equipment, material and time limitations. However, the tests were simple and practical, and hopefully answer the sort of questions asked by model engineers.

Tests were performed to determine the maximum depth of cut achievable by the Diamond tool before chatter/vibration began to occur. Of course, this also depends upon the rigidity and power of the machine used, as well as the tool itself. Additional aspects including sharpening and ease of setting up the Diamond Tool were also considered. 

The tests were done on the author's Viceroy lathe (Denford Machine Tools Ltd, photos 3 & 4). This is 5 inches to centre, 2 feet between centres, has an American-style V-bed, a ¾ HP motor, and a 4-way tool post. It is nearly 50 years old and had a 'hard time' in industry before the author bought it about 30 years ago. The mandrel is fitted with Timken taper roller bearings. These were replaced, together with the top slide and cross slide screws, soon after purchase. The gibs are well adjusted and there is no sign of play in the slides or mandrel. This is thought to be fairly typical of a model engineer's lathe.

For roughing or heavy cutting, the manufacturers suggest it is best to rotate the tool-post so that the tool point is trailing http://www.eccentricengineering.com.au/index.php?option=com_content&view=article&id=7&Itemid=32

This was done for all tests. The tool tip was sharpened between each material tested merely as a precautionary measure, so that there was no possibility of a test being affected by a previous test.

The materials on which the tool was tested are typical of those used by model engineers, as follows:

Free cutting mild steel (EN1A)

Silver Steel (Stubs)

Free cutting stainless steel (EN303)

Cast iron rod

Free cutting brass

Phosphor bronze

Aluminium (HE30)

White Delrin (polyacetal)

Wood (seasoned yew)

These were turned at the next lower lathe speed available than the recommended cutting speeds (ref. Model Engineer’s Handbook by Tubal Cain, and other sources). The maximum speed of the lathe was 1300 rpm and for some of the materials this was less than ideal. Manual feed was used in all cases to 'feel' the cutting action and provide a 'stop-start' chip break. The Diamond Tools was/is not provided with a chip break; indeed, it would defeat the object of making it easy to sharpen. The materials were turned dry except where indicated (Table 1). Various diameters of work were tested, depending on the availability of material. The cutting distance from the chuck jaws was noted; clearly this has an important influence on chatter.

The Diamond Tool bit was ground according to the manufacturers published instructions, using the jig provided, for all materials except free cutting brass. In this case, according to the manufacturers instructions (personal email), a small region of zero top rake was honed on the tool using a small oilstone (photo 5). This is to prevent 'dig-ins' and acts similarly to the zero rake applied to a twist drill when drilling brass.


TABLE 1

 

Key to Notes:


1     Trefolux cutting paste was applied using a stick to help prevent welding at the tool tip.


2    For free cutting brass only, the tip of the Diamond tool had zero top rake.


3    Maximum depth of cut = length of cutting edge of tool


Discussion

If one looks up lathe tools in any textbook on workshop technology the first thing one notices is that the tool angles are different for different materials and that there are a wide range of different tool shapes. How then can the fixed cutting angles of the Diamond Tool and its fixed shape be justified? The answer is quite simple: Textbooks give the optimum cutting angles for production engineering. This does not mean that other cutting angles will not work; it simply means that they may not be quite as efficient. Similarly, textbooks show a wide range of tool shapes, but for the majority of turning only a few are needed. 

As far as the model engineer is concerned, it is most unlikely that he or she will have a wide range of tools available. For example, if one looks in the Model Engineer’s Handbook, this lists cutting angles for 9 materials (two sets for each - roughing and finishing) and 7 basic tool shapes, that is 126 tools! Furthermore, it is unlikely that most model engineers have the equipment to accurately grind such tools. For most turning jobs, one can 'get away with' just a few tools. The author uses mainly two: a combined surfacing and facing tool and a parting tool (From now on, the author will be using the Diamond Tool in place of the conventional combined surfacing and facing tool).

In designing the Diamond Tool, Eccentric Engineering have chosen angles to suit the common materials used by engineers together with the most useful tool shape - the shape for both surfacing and facing at one tool setting. The only exception to using one tool for a range of materials is, in the author's view, brass. Cutting brass with positive top rake can be prone to 'dig-ins', particularly when using heavy cuts. As mentioned earlier, Eccentric Engineering suggests that if one is concerned about this, one should put a small zero rake on the top of the tool bit.


Referring to Table 1

The Diamond Tool performed very well on a wide range of commonly used model engineering materials. Silver steel has a reputation for being difficult to cut, so 0.10in. was considered very reasonable. Free cutting mild steel (EN1A) was a delight to cut with a very respectable 0.12in. depth of cut. These depths of cut are clearly limited by the lathe used – after all it is nearly 50 years old! The manufacture's video shows the tool in use on a newer, more robust lathe http://www.youtube.com/watch?v=xUAPrkC7Q-Q. In that case, when using free cutting, bright drawn, mild steel, the depth of cut is the full length of the cutting edge, or about 0.24in for the 1/4in. HSS tool bit used.

Referring back to these tests: the softer materials, such as aluminium, were obviously much easier to cut, and in these cases the depth of cut was limited by the length of the cutting edge (0.24in).

But Table 1 does not convey the whole story. Additional aspects that make the Diamond tool particularly attractive include:

Sharpening: Grinding lathe tools must be done on the periphery of the wheel and not on the sides of the wheel. The equivalent conventional tool has to be ground with three compound-angled facets. It takes a long time to acquire the skill to sharpen this sort of tool properly and safely. Grinding conventional tools is usually done freehand and invariably cutting angles are changed after several sharpenings. An important advantage of the Diamond Tool is that there is just one facet to sharpen and this is done using the simple grinding jig provided. Furthermore, the shape and cutting angles of the Diamond Tool are determined by the tool holder and grinding jig, and remain unaltered after sharpening.

Centre height adjustment: Sharpening a conventional tool alters the centre height, and bringing the tool to centre requires packings (at least when using a simple 4-way tool post). It is infuriating and time consuming having to sort out packings. The Diamond Tool does not require packings. The tool is set on centre merely by releasing the fixing screw and sliding the HSS tip up or down.

Safety: Would you put your fingers near a rotating milling cutter or near the work when turning!  But when grinding lathe tools fingers are perilously near the wheel. The danger is real; the author seen some nasty accidents using off-hand grinders. So anything manufacturers/users can do to minimise the risk, the better. As mentioned above, the Diamond Tool typically reduces sharpening from three compound facets to just one, and that is made easy using the simple grinding jig. In the author's view this reduces the risk of accidents considerably, and for someone new to sharpening tools that is particularly important.



Conclusion

The Diamond Tool performed very well on a wide range of commonly used model engineering materials. The tool is far easier to sharpen than a conventional tool and the optimum cutting angles are set automatically. For this reason the Diamond Tool is also considered safer to sharpen than a conventional tool. Furthermore, it is easier to set up and does not require packing to set the tool on centre. Hence, the tool is ideal for newcomers to lathe work as well as experienced turners.

In conclusion, the author considers the Diamond Tool an excellent product and now uses it in preference to a conventional tool. It should rank high on the model engineer's wish list.


Manufacturer:

Eccentric Engineering

P.O. Box 60

Mount Waverley Melbourne VIC 3149 Australia

http://www.eccentricengineering.com.au/


UK distributor:

 T Sneesby
 4 Carrwood Gardens
 Galgate
 LA20PB
 Lancs

http://www.eccentricengineering.com.au/index.php?option=com_content&view=article&id=17&Itemid=17


US distributor: Bay-Com

 

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