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10 Tumbler lever down travel is impededby contact with the casting.

15 Underside view of saddle shows “push– pull” adjustment screws.

12 After adjusting the motor position,clearance has been gained between thebelt and the headstock casting.

13 The diamond lap has been carvedaway at an angle to permit access to theroot of the dovetails.

11 Showing clearance between largerwhite gear and washer.

14 Raised metal around stamped numbershas been dressed off with lap.

27Christmas 2007

along the bed and off at the tailstock end.All that remains is to take off the secondleadscrew bearing and the leadscrew.

Examination and Reassembly Jingoistic humorists used to comment thatChinese machines were OK if you treatedthem as a kit of parts. It seems there isstill an element of truth in that view, atleast as regards the “Factory assembled”condition. It must be acknowledged thatthe manufacture is being undertakenusing decent production equipment, sothe inherent component quality is good. Itwould appear, however that the assemblyprocess does not benefit from the samecare and attention that one comes toexpect from say, a Myford.

This element of care and attention canthough be introduced by the new owner,who has a certain level of mechanical or

engineering skill and or is prepared tospend some time to read through variousarticles on this subject, as suggested earlier.

Apart from the notes above, the principalpoints of criticism relate to the cross andtopslide, where for each pair of slidingsurfaces, one is typically finely groundwhile the other is milled, showingsignificant machining marks. Here iswhere the traditional skilled machine toolfitter would scrape the slides to improveaccuracy and smoothness. I do not classmyself as having anywhere near therequired level of skill for this, so simplygave the milled surfaces a gentle rub witha fine triangular file and a small diamond

lap. The lap has been modified bytrimming away the plastic backing at anangle to allow it to get fully into thecorners of the dovetails, photo 13.

The first area to be dealt with is theunderside of the bed. The upper surfaceand vee way are ground all over, but thesides (which make no contact) and theunderside appear to be milled, albeit withgood finish. The diamond lap wascarefully held against the underside anddrawn along several times using lightpressure. This would remove any localhigh spots. A small area on the top surfaceof the bed was also given the laptreatment at this point.

The serial number is stamped into theupper working surface after grinding andthis causes metal to be raised around theedges of the numerals. Taking the raisedmaterial off with the lap left the number

still easily legible, photo 14 and improvedthe sliding action over this area. This areais unlikely to be used at the very end of thebed, but model engineers are notoriousfor stretching machine capacity so younever know. The lower working surfaces ofthe saddle were then coated with“Copaslip” (Arc use this) and the castingslid back on to the bed.

It may be useful at this point to add abrief description of the adjustmentarrangement. Two metal strips are pulledup to the underside by three Allen screws,relative thicknesses of bed and saddlebeing chosen so that pulling up tightwould clamp to the bed. Jacking screws

with locknuts are also fitted and thesefunction to push the strips downwards andset a working clearance. The arrangementmay be seen in photo 15. Thus the

adjustment sequence is a repetitiveprocess of lightly adjusting the opposedpush - pull actions to achieve a good fitand feel. It should be noted that firmtightening of the pull up screws is notrequired and in fact, if overdone(according to web notes) may actuallycause fracture of the strips.

Attention then moves to the apron,leadscrew and associated bearings. Here,Arc drills an oil way and adds internal oilgrooves. Many owners may choose not tomake this change and rely on oiling fromthe bearing ends. However, it probably willresult in extended life.

While it would be possible to do thedrilling on the C3 using the milling

attachment, as the lathe was in pieces, thesimpler alternative was to use the VMCmill. Photo 16 shows the RH bearinggripped in the vice canted up 45 degreesand a piece of thin sheet brass used underthe point of the drill to get close to thecentre of the curved surface. (When thebrass was horizontal, the drill was close tothe centre.) The bearing length is 20mm sothe hole was drilled 10mm from one end.

Following the Arc example, a Minicraftdrill with a small burr, was then employedto cut a diagonal oil way within thebearing. The 45degree cant mentionedwould ensure that the oil hole would beconveniently accessible after assembly. A

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16 The RH leadscrew bearing being set upfor drilling an oil way.

17 Inside view of the apron showing the half nuts and gears.

18 Milled surface of the cross slide dove- tail is lightly rubbed with the lap.

19 Showing the step filed to ensure cor- rect movement of the tumbler assembly.

20 The tumbler bracket is a pressing withsharp edges on one face.

22 Shows the burr raised by the tailstockhand wheel grub screw 

28 Model Engineers’ Workshop

similar series of operations was carriedout on the LH bearing.

Attention was then given to the apronassembly. The half nuts were removed,and their respective dovetails given a

touch with the lap. These, the shafts andthe gears were reassembled with moreCopaslip, photo 17. With the bearings andleadscrew also given a dose of Copaslip,the LH bearing with leadscrew could bejury rigged. The apron (with clasp nutsopen) was then carefully threaded over theleadscrew and loosely attached to thesaddle. After fitting the RH leadscrewbearing, the screws holding the LH weretightened whilst pressing the bearingtowards the right. Similarly, the RHbearing was nipped up whilst applyingpressure towards the left. (The reason isthat the leadscrew end float is set by therelative positions of the two bearings and

this sequence aims to minimise this.)Now the saddle and apron are moved

as far as possible towards the righthand end of the bed. The half nuts arethen closed, and the two bolts securingthe saddle to the apron areprogressively tightened. (The securingbolts pass through elongated holes andthis procedure sets the apron positioncorrectly in relation to the leadscrew.)

As a final check in this area, with thehalf nuts still closed, the RH leadscrewbearing bolts may be slackened andretightened, again pushing to the left.This will allow it to move up or down afew thou to centralise the leadscrew onthe half nuts.

Apparently, it is not unknown for the rackposition to be less than perfect, resultingin poor meshing of the carriage gear teeth.If necessary the rack may needrepositioning for optimum engagement.

The lap was again brought into play forthe cross slide and top slide dovetailsurfaces – just a gentle rub to clear anyhigh spots, photo 18. The cross slide with

its lead screw, bearing and handle werethen added, again with a measure ofCopaslip lubricant. The gibs on these

slides are relatively thick (about 4mm) andadjustment is by socket head grub screwsand locknuts. These screws have dogpoints which locate closely in drilledrecesses in the gibs. It was found thatthere was some reluctance to re-engagewith the recesses, and so the screws wereeach given a very light chamfer on the dogpoint. (Out of interest, G H Thomasrecommended that gibs be pinned, and it

may be argued that this arrangementgives much the same effect.

When rotating the topslide, a notableclunk could be felt (and heard). This turnedout to be another case of metal raised bystamping (after grinding), in this case thefiducial mark for angle setting. Once again,a few strokes with the lap effected a cure.

The alloy belt cover was then refitted.Before adding the tumbler bracket, a smallamount of metal was filed away from thefoul point mentioned above. The tumblerwas then fitted, ensuring that clearanceexisted between the nylon gear andwasher mentioned earlier and shown inphoto 11. Metal was also removed from

the cast carrier, photo 19, which was thenrefitted along with the associated gearsafter lubricating the bearings.

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21A The gear alignment has been improved -- 21B --- by the addition of a washer.

23 The grub screw on the carriage handwheel has a drilled recess. 24 Assembled and under power.

29Christmas 2007

Examination of the changewheel bracketshowed this to be a pressing, photo 20 with

sharp edges on one side. These weredressed off with a file before the bracket withwheels was added, after locating a singlewasher behind, which would bring the gearsinto better alignment, photos 21A & 21B.

The tailstock upper and lower sectionswere not separated at this stage althoughthe barrel and screw were removed forlubrication. While this was in pieces, theopportunity was taken to lightly chamferthe end of the barrel, removing a sharpishedge. It was also noted that the handwheel is retained by a cup point grubscrew which had marked the shaft, photo22. The marking was dressed away with afine file, and a small brass disc inserted

below the screw. In contrast, the carriagehand wheel is held by a cone point screwand in this instance, the point locates in a

drilled recess, photo 23.Fitting the change wheel cover, splash

back and chuck guard completed theexercise after which the machine was firedup, photo 24 running the saddle underpower feed backwards and forwards severaltimes to check operation. Operating thevarious slides manually was now noticeablysmoother compared to the earlier, asreceived “Factory assembled” condition.

Whilst this was my experience of the“Factory assembled” model, I understand

that Arc’s in house preparation processmay find other “variables” which mayneed to be looked at. Any that do arise willbe covered on Arc’s website in due course,under their projects and articles section.

In the next article, the machine willbe put to work, and some of theaccessories will be described.