Sunday, December 22, 2013

Raglan Little John Mk.2 Bench Lathe - Post 6 - Fitting an alien steady rest (fixed steady or center rest)

1. Introduction

The fixed steady (or in other wording the steady rest) is usually optional equipment for the bench lathes. However, the steady rest could be proven quite handy for specific projects even for the bench lathe, especially in cases of processing long, thin and light materials susceptible to vibration during metalworking. Given that nor RAGLAN neither their successors at MYFORD are in business any more, steady rests (or any rests for that matter) for Raglan Little Johns are nowadays quite rare, so -in case of need- one might have to construct his own or adapt one available from the market. For our situation, it was decided that it is worthy to give it a go with the second choice, since the machining capacity in the little shop is somewhat limited and available time is precious. In this post, I will try and review in detail a serial process of fitting the alien steady rest to our Little John, productively and efficiently. The whole project is estimated to cost approximately something like 70,00 EUR or about so and no more than 10 hours of work at a quite relaxed pace. The necessary tooling and materials are: drill press, hand drill, twisted drills of various diameters, M6x1.0 taps, M6x1.0x30 mm allen bolts (hex socket and countersunk socket heads), files, a hacksaw, angle grinder (maybe) and, of course, the steady rest to be adapted. For a more precise metalworking a mill drill, or lathe milling attachments or even a milling machine is necessary. The whole project may be completed also without any milling, however, at a higher time and hand metalworking cost.

2. Looking for the suitable steady rest in the market
    
The bench lathe accessories available in the market, are predominately Chinese made. For this project one should look for accessories of well-known quality, suitable for bench lathes with similar dimensions to these of the Little John. In my point of view, such bench lathes could be -among others, the Optimum Maschinen GmbH types D240x550/D250x550 and the Model C6 Mini Lathe, now (2013) known as the SIEG Super C6 lathe. Both lathes have a "swing over bed" capacity of 250 mm much similar to the Little John's 10". To my best of understanding these two lathes share common components, which have been designed by the same team and/or are probably manufactured in the same Chinese facilities. Here are the respective pictures of the steady rests available for  these lathes:

(a) For the Optimum D240x550/D250x550 and according to their catalog:

Fig. 1 Steady rest for the Optimum bench lathe
 For the lathes in question a(max.)=55 mm; b=250 mm; c=140 mm.

(b) For the SIEG Model C6 (or Super C6) Mini Lathe:

Fig. 2 Steady rest for the Super C6 Mini Lathe
For this rest a(max.)=63 mm, no other dimensions are specified.

Such rests when in work, look like this:

Fig. 3 Steady rest of type (a) or (b) in work; follow rest can be also seen on the left
(image taken from en.makepolo.com)

Following the particulars of the Greek market, it was much easier to obtain the first follow rest (part number 3441315).

3. Modifying the selected rest

Having in mind what the steady rest's job is, its suggested position relative to the cutting tool and the available space and other particulars of the Little John lathe, it was necessary to face out any bed ways respective formulation on the base of the rest. This was accomplished at the mill. Caution was exercised not to apply excessive metalworking forces since the rest's profile has thin parts susceptible to breakage. Here is a series of pictures presenting this project stage in detailed steps:

Fig. 4 The steady rest dismantled and before any intervention

Fig. 5 The steady rest on the mill in the process of getting rid of the base formulation
Fig. 6 The steady rest on the mill; note the additional wooden plates vice improvisation used
for securing rest's thin cross sections from breakage
The wooden splint precaution has been taken to support the thin part of the rest's profile from breaking, due to possible milling excessive forces.

Fig. 7 Front view of the steady rest on the mill after milling
Fig. 8 Front view of the steady rest on the mill after milling; wooden splint removed and
a new base surface is set
 4. Preparing for the fitting

Having done the initial modification of the rest, it was time to find out what is the rest's center height  in relation to the lathe centers. To this end the tailstock and  a kit of 3 mm thick parallel plates were used. Here  is how it looked:

Fig. 9 Rest's center height in relation to the lathe centers

It was found that approximately 15 mm (5 parallels) should be added over the lathe's bed surface so that the center of the rest could acceptably level with the axis of the lathe. With this information in hand, the following mild steel DIN 1017 flatbar ("b" wide" by "s" thick) pieces were purchased:

(1) b=50 mm, s=20 mm of length=85 mm, and
(2) b=40 mm, s=15 mm of length=85 mm

Piece (1) was acquired to be machined as height adapter. It was selected to be 50 mm wide, since the rest's base available was somewhat less in width. Further, it was selected to be 20 mm thick under the plan that the new modified base should fit with precision, within the ~5 mm deep gap between the bed ways. If one adds this depth to the 15 mm needed to align the rest's center to that of the lathe gets a sum of 20 mm. Piece (1) was selected to be 85 mm long, in order to allow enough thickness for precision machining down to the exact width between the internal bed ways sides, which is approximately at 3 3/16" (or ~80.3 mm)

Piece (2) was acquired to be machined as clamping plate. It was selected selected to be 85 mm long, since the clear internal distance between the sides of the lathe body is around there; some attention should be paid that the bolts and nuts securing the bed ways on the lathe body actually determine this distance; measuring the internal distance of the cast iron body is not accurate for the purpose of this project.

5. Machining and bench work - part I

Firstly, one had to drill a couple of 6 mm wholes in piece (1), so that to prepare it for attachment to the rest, as a height adaptation to needs. Part of the wholes length were made wider pockets at 10 mm of diameter, in order to sink and hide the allen bolts heads, needed for securing the adapter to the rest.

Fig. 10 Drilling of the height adapter

Secondly, since piece (1) is to be attached underneath the rest as it had been milled, the position of these holes had to be copied to the base face of the rest's body. Therefore, a -not as precise- copying trick was applied:

Fig. 11 Copying drill holes positions trick
Subsequently, rest was carefully positioned on the drill bed and the copied drill hole positions were drilled through using a 5 mm drill, to allow for a 6.0x1.0 mm thread tapping later on. Note that, due to the casting model, rest's base back face is not parallel to the machined face. Therefore, vicing it in position was not that straightforward.

Fig. 12 Drilling rest's base with a 5mm drill at predetermined positions
After the successful drilling, some hand tapping took place:

Fig. 13 Hand-tapping M6 threads in holes
Following tapping, the height adapter was finally bolted to the rest. However, the center hole allowing for the bolt necessary for the connection of the clamping plate was still not in place. So, back to the drill it is. Luckily, a long 12.5 mm twisted drill was readily available in our tools collection.

Fig. 14 Copying central drill hole position to the height adapter
After marking the central drill hole position, the height adapter was dismantled and the hole was finalized at the drill press.

Fig. 15 Finalizing the central drill hole position on the height adapter
All pieces (rest and height adapter) were then thoroughly cleaned. It was decided that tightening the bolts might not be enough in the trembling lathe environment, therefore, bolts, which are not meant to be removed from this point and on were further secured using a product similar to LOCTITE 222.

Fig. 16 Securing the bolts connecting the rest with the height adapter
using appropriate glue
The intermediate product is presented in the following photograph.
 
Fig. 18 Midway to the final product
6. Machining and bench work - part II

Both long sided faces of the height adapter were then machined on the mill, so that to be worked down to the actual width of the rest base itself. This machining was done clearly for visually aesthetic purposes and no actual precision was really needed there.

Fig. 19 Aesthetic machining of the height adapter right long side
down to the width of the rest base; same for the left long side
After this, the intermediate rest was adequately rotated to allow for the precision machining of both of the height adapter short sides.

Fig. 20 Precision machining of the height adapter short sides
down to the width of the rest base; same for the left side
The aim of this precision machining was to construct a piece with length exactly equal to the parallel gap between the bed ways of the Little John lathe. This gap has been measured to ~80.3 mm. Unless exact means of measuring milling cutting depth are readily available, during such machining procedures, one has to have in mind that:

(a) Cutting tools and procedures of average conventional workshop machinery are precise up to a point. A safe limit is in the range of 0.05 to 0.1 mm. This limit can get closer to 0.05 mm depending on the experience of the machinist handling the equipment. Claims that this limit could be systematically pushed down to less than 0.05 mm, do not hold much water.
(b) Machining  mild steel may sometimes present inaccuracy in cutting, mainly due to lower yield as compared to other kinds of steel containing more carbon. As a result tools cut randomly more and deeper than set.

Taking into consideration the above notes (a) and (b), when approaching the final requested dimension, the rest was repeatedly removed from the mill and tested for fitting in the gap. The whole procedure allowed for a precise length machining to meet the purpose of the project.

7. Clamping plate preparation

Piece (2)  was subsequently machined as the clamping plate. First step was to drill the appropriate 12.5mm hole for the central bolt of the steady rest.

Fig. 21 Drilling a central 12.5 mm diameter hole was the first step
of the clamping plate machining
Using this central hole, piece (2) was mount on the Little John's chuck. The sides were then machined so that the diameter of the piece could become approximately 83 mm. This  diameter provides enough clearance for the plate to revolve around the rest bolt without any interference from the sides of the lathe body.

Fig. 22 Finalizing the outside diameter of the clamping plate to ~83 mm
The clamping plate was then introduced to the mill, for the construction of a channel wide enough to host the non-standard head of the rest's bolt. The channel was machined to 8 mm depth and 22 mm width. A two flute end mill was preferably used for the cut, since this works better with mild steel.

Fig. 23 Making of the channel to host the head of the rest's bolt

Fig. 24 The non-standard head of the rest's bold
Having finished with the bolt head hosting channel, attention was paid to the other side of the clamping plate, where, naturally, it was necessary to cut steps so that the clamping plate could be tightened firmly to the lathe's body, thus securing the rest into position. The steps where also 8 mm deep and 6. mm wide, if width is measured at the diameter of the clamping plate. This results to a clamping plate length between the steps, of about 71 mm.

Fig. 25 Cutting steps on the clamping plate
8. Final product

Finally, the finished  steady rest can be seen in the next few photographs.

Fig. 26 The finished steady rest (view from "left")
Fig. 27 The finished steady rest (view from "right")
Fig. 28 Primer application before final corrective paintwork
Fig. 29 The steady rest's parts reassembled

Fig. 30 The steady rest in position

9. Some remarks (most of them also in Post 5)

Original Little John's fixed steadies are certainly rare; their pictures are rare as well. In order to present an idea how the original steady looked like here is an image found on the net:

Fig. 31 Little John's original fixed steady
(travelling steady also seen at the right)
This  images can give an idea on how the original could be placed and work on the little John lathe

Some other relevant  images can be also found in the RaglanMachineTools Yahoo Group (in http://groups.yahoo.com/groups/RaglanMachineTools).

I had recently a personal communication with this Yahoo Group moderator Mr. John Burridge (John.Burridge@fsmail.net). He let me know that he has been making steadies for the Raglan lathes, both fixed and travelling and also an extended fixed steady of 150mm capacity (6"). He has the drawings and he can get castings of them, which in turn can be machined and finished.

9. Rights and citations

Copyleft protects this post. This means that you may freely copy and distribute this content but please do not change it. If you, in the process, find that something in this post is inappropriate or wrong, please contact me at my e-mail. I would be more than happy to update the post. You are more than welcome to site this post in your own texts, blogs or whatever. If this is the case, please use more-or-less the following citation format:

Petropoulos, N.P., "Raglan Little John Mk.2 Bench Lathe - Post 6 - Fitting an alien steady rest (fixed steady or center rest)", 2013; add URL; add access date.

Any citation will be much appreciated.