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+--- Thread: Modifying 13 Inch South Bend Steady Rest to Fit 11 Inch Sheldon (/thread-3637.html)
Modifying 13 Inch South Bend Steady Rest to Fit 11 Inch Sheldon - randyc - 07-29-2017
NOTE: most of this will already be known to experienced members, excessive details are intended for those who may not have your background.
After spending some time searching for a 1940’s era Sheldon steady rest, I concluded that chances of locating an original were slim. And if some miracle occurred and I located one, it’s unlikely that the cost would be acceptable. (From what I see on eBay, even the most common ones go for around $200.)
Through an unrelated acquisition, I had an old 13 inch steady rest that appears to be made for a South Bend machine. I’d intended to use it for a trade but why not modify the thing ?
After all, it would save a lot of $$$ and would only take a couple of hours, right ? We all know how THAT goes ! The first step was to bead blast the old steady to remove the muck and rust before starting work.
Propping the steady rest on the Sheldon’s ways and making careful measurements, the centerline of the South Bend steady was noted to be about an inch high and an inch offset from the spindle centerline of the Sheldon. The base of the steady of course didn’t match the ways of the Sheldon.
Based on measurements, the lower portion of the S.B. steady rest was sawed off to accommodate differences in height plus the thickness of a new base plate that fit the Sheldon lathe ways. (The horizontal position of the steady had to shift as well.) In this photo, the base of the South Bend steady rest has been sawed off - this is clearly the point of no return:
[attachment=14665]
The next step is to make a new baseplate. The Sheldon lathe, like most larger lathes, have male “vee’s” machined on top of the ways to locate the carriage and the tailstock so that they are parallel to the spindle centerline.
On older machines, the carriage ways are usually worn more than the tailstock ways near the headstock because the carriage is generally used more often than the tailstock.
Since the Sheldon was made in 1945, there was discernible wear on the carriage ways so the baseplate was designed and machined to fit the tailstock ways, these showing much less wear.. After cutting an appropriate length from ½ x 4 inch mild steel stock, the blank was set up on the vertical mill.
The workpiece was positioned in the vertical mill at 45 degrees to the cutting tool axis. This must be done accurately to fit the 90 degree “vee” on the Sheldon ways. The workpiece was adjusted to the correct angle using two precision ground angle plates, a 15 degree and a 30 degree plate, wrung together (there is no 45 degree in my set of angle plates).
It can be seen that this wasn’t a very rigid, secure setup so feed and the depth of cut had to be modest. (The cutter was a 5/8 diameter, 4-flute cutter run at about 500 RPM; sulphur pipe cutting oil was applied with a flux brush, DOC was about .050 inches, feeding the table slowly by hand.)
[attachment=14666]
After milling the “vee” groove, vacuuming away the chips and wiping off cutting oil, this is the baseplate before drilling a couple of 9/16 mounting/clamping holes.
[attachment=14667]
Next, the steady rest and the baseplate had to be aligned before securing them together. The photo below depicts the alignment method.
A scrap piece of stock chucked in the lathe was turned to about one inch diameter; the dimension is not critical, the point was to establish a cylindrical surface accurately centered on the lathe spindle centerline.
The jaws of the steady rest were snugly adjusted to fit the turned piece in the headstock, carefully aligning them so that the steady rest was centered on the test piece. The steady rest was then fairly well aligned, the base plate was placed under the steady rest. The two parts were then tack welded together.
[attachment=14668]
The tacks were located on two opposite sides, maintaining the alignment of base to steady rest. The assembly was removed from the lathe and finish welded. This is a VERY tricky operation because the mild steel base and the cast steady rest have two different rates of thermal expansion and two different rates of cooling.
MIG welding is not recommended for castings and when it is used, the parts are pre-heated – maybe even until they are glowing dull red then, after welding (using nickel wire, I believe) cooled very slowly. A typical cooling method is burying the weldment in sand and waiting for a day or so.
Doubtless, most of you already know that welding cast iron, especially to a wrought piece of steel, is a bad idea. For those who don't know, the reasons are as follows:
At normal room temperature, as the joint cools after the intense heat of the welding rocess, differential contraction of the parts can produce enough stress to cause the cast iron part to break.
The time-tested procedure of joining cast parts is bronze welding (brazing) which takes place at a lower temperature than steel welding. The advantages are a certain amount of flexibility in the joint and a more evenly distributed temperature throughout the two parts. This is the tack welded assembly preparatory to cleanup and finish welding.
[attachment=14669]
After some internet research, I decided to try a process alleged to be a successful technique of joining cast iron to steel using a MIG welder and .030 mild steel wire rather than torch brazing. (Torch welding/brazing/cutting was formerly not a problem for me but my aging, neuropathic and shaky hands now make such tasks difficult.)
To minimize my shakiness, I rested my hand on a nearby surface and triggered the MIG torch briefly. The recommended technique was to apply a series of tack welds along one side of the casting, peening immediately (I used an air-powered needle scaler) and allowing the assembly to completely cool between tack welds.
That is what I did, first welding along one side of the steady rest and then the other in short tacks. The part was not heated except locally so there wasn’t the major problem with differential contraction as would occur with stringer welds. Although there wasn’t a lot of welding to be done, I was conservative and did the welding over a four hour period, allowing long cooling periods.
[attachment=14672]
So far, so good, the joints visually appeared to have integrity although the series of tacks was not particularly pretty ! Since the steady rest was to be painted to match the lathe, I ground the welds and filled irregularities between the tacks with JB weld.
The next step was making a clamping plate (this part fits under the ways). A ½ - 13 bolt was welded to the machined clamping plate.
This nasty tack weld was a result of misplacing my welding helmet. Impatiently I positioned the MIG torch, gripped the end of the bolt with the welding ground clamp, closed my eyes and squeezed the trigger.
[attachment=14671]
This obscene result is due to my shaky hands and no visibility. I ground the weld out and repeated it after finding my helmet, then tacked the other side of the bolt head. Unfortunately I didn’t photograph the better-looking result. More to the point, the above photo depicts the shape of the clamp.
The plate is angled on two corners because of functional requirements. Rather than inserting the clamp plate from beneath the lathe ways and then bolting it to the steady rest, this design was intended to allow the steady rest and the clamping plate to be permanently attached to one another.
Rotating the clamp plate enables it to be withdrawn between the two sets of ways on the lathe. This is effected by rotating the stud of the clamping plate clockwise by 90 degrees which allows the entire assembly to be easily removed through the gap between the ways.
(If the corners were not angled, they would be obstructed by the interior shape of the lathe bed casting and wouldn’t rotate into the proper position.)
This is the clamp plate in locked position. The lower nut clamps the steady to the ways. The upper nut (which is loctited to the clamp stud) is used to rotate the clamp after loosening the lower nut, allowing the steady rest to be removed.
[attachment=14673]
After painting and positioned with a test workpiece:
[attachment=14674]
Finished it on Friday - works good - but it did NOT take a couple of hours, like I estimated, ha-ha-ha !
Cheers,
randyc
RE: Modifying 13 Inch South Bend Steady Rest to Fit 11 Inch Sheldon - Mayhem - 07-29-2017
Nice job Randy.