building a 120mm rotary table

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Building a 120mm Rotary Table Dean Williams (www.deansphotographica.com) has a webpage describing his projects. One ofthem is building a 4 in. Rotary Tablefor his Taig Mill. Dean used a pieceof hotrolled 4 in. square tubing forpart of the rotary table base. I wanteda slightly larger table so I used apiece of 120mm square tube instead.This way it should be possible tomount a 100mm chuck on the table.Unfortunately, the square tube Imanaged to find was rather thin-walled compared with his, so I had tofind another way of attaching the topof the base to the square tube. I alsodeviated from Dean’s description inother areas, for once I made the tablefrom two pieces bolted together.

Materials Besides the square tube I managed to get an off cut from a 120mm diameter steel rod for free, I usedthat to make the lower part of the table. The top of the table was hacksawed from a piece of 10mmthick steel plate. I friend gave me a piece of brass for the worm wheel and I bought a cheap ball bearingand some Allen screws. The rest was pieces from my scrap box.

Base I started with the base, I milled the outside of thetube to get it as square as possible, I don’t haveany plans to mount the rotary table in the verticalposition and use it as a dividing head, I alreadyhave dividing heads. The tube was mounted on the milling machinetable using three angle plates, this way the topshould be square to the sides after milling – seeright photo.

Since the square tube was thin walled (about 4mm) Ihad to screw and solder 4 pieces of steel at the top ofeach corner. The joints were fluxed and with thescrews tight the four pieces were silver soldered (hardsoldered) to the tube, just beneath the top surface.

After silver soldering I could use the corner pieces toclamp the base to the faceplate – left photo. Now the

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bottom could be faced parallel to the top of thesquare tube. The tube was now squared and the nextoperation was to mill a couple of slots in the lowerpart of two of the sides, these slots will be used forclamping the rotary table to the milling table. To prevent swarf from entering through the slots Idecided to epoxy and screw two pieces of 8mmthick steel on the inside of the tube before millingthe slots – right photo.

The slots were milled with an 8mm slot drill to adepth of about 8mm – left photo.

The holes in the top of the base was marked outand the holes drilled and couterbored, the topwas clamped to the square tube and the pre-viously drilled holes used to spot the holes in thesoldered corner pieces. These were drilled3.3mm and tapped M4 – right photo. It was now possible to clamp the bottom of thebase to the lathe faceplate and take a light facingcut on the top of the square tube to get top andbottom surfaces as parallel as possible – rightphoto.

The next job was to mark out the centreof the top plate and clamp the base topplate to the base and take a facing cutand drill a pilot hole through the centreof the top plate. On the underside of thetop plate there will be attached a pieceof steel 8mm thick, all sides about65mm long. The top plate must beturned around and the hole turned to52mm (O.D. of ball bearing) from thebottom side, as the last 3mm of the holein the top plate will only be about48mm in diameter. This will prevent theball bearing from popping through the


hole in the top plate should the fit be a tad tooloose. The spigot on the table has the bottom endthreaded for an adjusting nut, so some preload canbe applied to the ball bearing. . The Base Top Plate was removed from the base.The Table Bearing Housing was drilled close toeach corner and countersunk. A pilot hole of thesame size as in the Base Top Plate was drilled atthe centre of the Table Bearing Housing. The pilothole was used to line it up with the Base Top Plateso the four clamping holes could be spotted andtapped. The assem bly was mounted on thefaceplate and centred using a drill in the pilot holeand a Dial Test Indicator. The pilot hole was opened up with larger drills, Istopped at 16mm as that is the largest drill I havewith a plain shank that fits in my tailstock drillchuck. The hole was then bored through, out to adiameter of about 48mm. The bottom 15mm wasthen bored out to52mm so the bearing was a lightpress fit in the hole – see right photo.

This is how it looks after the TableBearing Housing is finish turned andbolted and glued to the Base Top Plateand the Base assembled, with the ballbearing mounted and the inside given acoat of primer. The hole seen in the top right part ofthe Base is the hole for the worm shaft. The corners of the Base Top has notbeen rounded yet, that was the lastoperation to be done on my belt sander.

Table The table was fabricated from twoparts, the bottom was an off cut from a120mm diameter steel bar, with a10mm thick steel plate bolted andglued on top. The "T-slots" were milledin the top part, with the future bottomfacing up a slot about 15mm wide and5mm deep was milled. The holes forthe M6 screws were spotted from thelower part of the table. After the twoparts and the spigot were mounted, a10mm slot drill was used to mill theupper parts of the slots. I started by fabricating the spigot thatwill be bolted and glued to the underside of the table. The spigot is madefrom a piece of 30mm diameter steelrod and a small piece of steel platefrom my scrap box – right photo.

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After silver soldering (brazing)and pickling the work wasmounted between centres andturned slightly oversize. Theflange was turned to dimensionon the outside and faced to justunder 5mm thick – right photo.

Four 6mm holes were drilled inthe flange, spaced 90 deg. apart,they will later be used to spot thecorresponding 5mm holes in thebottom part of the table.

The bottom part of the table was mounted inthe 4-jaw and centred, one side faced. Thenturned around and the other side faced and thegroove was cut using a parting off tool. After facing a recess was turned to a depth ofjust over 5mm so the flange of the spigot justfitted, and the four holes in the flange used tospot the 5mm holes in the table – right photo.The table was then removed from the 4-jawand the four 5mm holes tapped M6. The 6mmholes in the spigot flange was countersunk onthe spigot side. The spigot could now be bolted to the bottompart of the table and mounted in the 4-jawagain. I had previously checked the 120mmdiameter offcut used for the bottom part of thetable, and it was pretty round and smooth onthe outside. So after clocking it in the 4-jawthe turned part of the spigot runout was about0.01mm. There probably is a better way ofdoing this, but it worked for me. The under-side of the table was given a light facing cut

and the spigot turned to 25mm for a push fit in theball bearing. The rest of the spigot not being"occupied" by the ball bearing was turned downslightly to a sliding fit in the hub that will carry thewormwheel, and slightly more at the very end wherea 1.5mm pitch thread was cut for the nut that adjustsaxial play. The position of the 6mm countersunk holes weremarked and drilled/countersunk, and used to spot thecorresponding 5mm holes in the upper part of thetable. After the two parts of the table was glued andbolted together the outside of the top part was turnedto the same diameter as the bottom part of the table.The bolts were cut to a length such as they protrudedabout 0.5mm above the surface of the table. The topwas then faced – left photo.


The work was reversed in the 4-jaw and Imounted my Headstock Dividing Attachment onmy lathe so I could make the 360 divisions aroundthe lower part of the table – right photo and below.

I just mounted a V shaped tool in my boring barand used a carriage stop to get the length of thedivisions correct. I marked the 36 ten degreesmarks first, then the 5 degrees arks slightly shorterand so on. The result is shown in the upper leftphoto.After making the clamps and the hub that carriesthe wormwheel and the adjustment nut I could

mount the table on the base and mount the hole onthe milling machine table and mill the upper part ofthe T slots using a 10mm slot drill. A slot drillmight not produce as accurate a slot as a slot drill,but I wanted the slot slightly wider than 10mm so Itook a light cut along each side after cutting the slot. I had made a simple Pillar Tool inspired by the oneGeorge Thomas made and used that to punch thenumbers – left photo.

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Worm and Worm wheel The worm wheel (60 T module1) should have been made byhobbing, I cheated and just usedan ordinary home made gearcutter and plunged it into thebrass disc I used to make thewheel. This doesn’t produce aproper worm wheel but in myshop the Rotary Table will notsee daily use so I guess it willlast my lifetime. To get the centre line of theworm wheel at 90 deg. to thecentreline of the worm the teethon the worm wheel must beangled, same angle as theworms helix angle. To achievethat I used a Sine table I madeearlier and mounted my dividing head onthe sine table.

Since the piece of brass used for the wormwheel on the thin side it would end up tooclose to the ball bearing and wouldn’t leaveenough room for the worm, I made ahub/spacer and mounted that together withthe worm wheel to get the width needed. Ialso made an arbor with a MT 2 shaft so Icould mount it in the dividing head – rightphoto.

The worm was turned from a15mm diameter mild steel rod –right photo. I made the worm in one pieceand turned it between centres. Thelength was just measured out to fitthe pieces from my scrap box thatwas used for the bearinghousings. Each end is turneddown to 10mm, to fit into theOilite bushes. I used Oilite bushes pressed intothe steel bearing housings. Idrilled oversize holes in thebearing housings and used theseholes to spot the holes in the basebefore drilling and tapping them


M4. Since the holes in thebearing housing are oversize itis possible to make smalladjustments and take up wear inthe worm and wheel.

The handwheel was turnedfrom a piece of 40mm diametermild steel rod from my scrapbox. If I find time I might turn asleeve to make a dial.

The finished handle, bearinghousings, worm and wormwheel.

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building a 120mm rotary table

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