04-09-03 16:36
No 425109
      Glass Blowing Lathe and Chuck
(Rated as: excellent)

Mechanically inclined bees may find this of interest smile

J. Sci. Instrum. 21, p. 17 (1944)

The object of this contrivance, illustrated below, is to provide a means of doing certain glass-blowing jobs which often arise in a laboratory and normally require skill and experience. Unless the art, of working glass is frequently practised, technique rapidly deteriorates, and it is then that this machine is especially useful. It has been made largely from scrap and such odds and ends as could be got together. The general idea is that there must be a means of sup­porting the horizontal glass tubing at each-end and revolving it slowly and evenly while heat from a gas flame is applied locally at one or more points, with provision made for blowing into the tube if required. It must also be possible to shorten or draw out the glass tube when softened by heat and to handle tubing of various diameters and lengths (within practical limits). These conditions are realized in the way described below.
Two 3-in. self-centring chucks are screwed facing each other to the ends of two co-axial horizontal tubular spindles (gas pipe carefully turned to 1 in. external diameter) which are supported in pairs of bearings as shown in the figure. An inch plank, 9 in. wide and 3 ft. long, carefully planed so as to have parallel sides, is screwed to a wooden base. At the left-hand end it carries two fixed substantial wooden columns 6 in. high, on which the bearings are mounted. At the right-hand side are two other wooden columns which stand upon a saddle that can slide upon the plank and be moved by a string fore and aft attached to winders. The distance between the chucks can be varied in this way; the maximum separation is 14 in.
The chucks are driven by cycle chain over 48-toothed bicycle sprocket wheels from a light countershaft which carries two small bicycle sprocket wheels each having 16 teeth. One of these smaller wheels is fixed to the shaft and the other is capable of sliding along it. Since the sliding sprocket wheel must continue to revolve equally with the fixed one while it is being moved forward or backward, it has a longitudinal slot cut in its centre which engages with a 1/8-in. metal rod sweated along the shaft. Thus for any position (within limits) of the movable wheel upon the shaft the two always rotate together. A metal arm projecting from one side of the saddle engages with a groove in the circumference of the boxwood centre of the movable sprocket wheel, so that if the position of the saddle is changed the sprocket wheel moves correspondingly and the chucks continue to to at exactly the same speed.
The countershaft is carried in bearings made from bored brass tea brazed to the top of a pair of shelf brackets. It is belt-driven a 1/4 h.p. electric motor, the speed of which is controlled by a variable resitance consisting of two carbon rods from torch batteries lowered into a weak solution of common salt. 40 r.p.m. seems to be the best working speed. Many simple operations can be done by the machine with great neatness, such as joining two glass tubes, drawing down a large tube and sealing a smaller one to it, etc. If, however, a bulb is required a small tube has to be sealed into position within a larger one, as instance in the case of a mercury trap or a filter pump, it is necessary be able to blow into the glass tube when it is softened locally and steadily revolving.
For this purpose the device described below is fitted to the left­band spindle. Into the end remote from the chuck a solid wooden cylindrical bush 3 in. long is tightly fitted and bored so as to take a two in. length of 1-in. brass tubing. This can therefore be pushed ally into the hollow spindle through the wooden bush and fixed
position by a set-screw. At its inner end a sweated-in nipple enables a narrow rubber tube to be attached, and pass into the spindle as to project for a couple of inches beyond the open jaws of the chuck. A glass tube pushed into the free end of the rubber tube can drawn into the chuck by releasing the set screw and pulling the brass tube to the left, thus drawing the rubber tube through the chuck bto the spindle and enabling the chuck jaws to be closed down lightly but firmly upon the glass tube itself. Since all rotate together when the machine is started up, it is necessary to find some way of blowing into the brass tube while it revolves. This was done by sweating a small brass plug into the left-hand end of it (which is beyond the spindle) and boring it with a widely tapered hole into which the conical end of a short length of metal tubing was pressed by a horizontal spring held stationary. One can by this means blow down the fixed tube {through a length of rubber tubing for convenience) into the glass tube held in the chuck; the fixed tube is not shown in the figure. The right-hand end of the glass tube being sealed up with a cork or by heating it and the distance between the chucks reduced, it can be gripped in the right-hand chuck, and all is ready for the work to proceed. If the machine is then switched on and a blow-pipe flame used to soften the central portion of the glass tube, the saddle may be moved forward and the glass allowed to thicken in the well-known way and, when sufficient "metal" has accumulated, a light breath into the tube causes it to enlarge evenly. The saddle may be finally and slowly drawn back as the glass expands and a graceful pear-shaped bulb is obtained. Numerous modifications of this method will of course suggest themselves, depending upon the requirements, but thistle funnels and much other glass apparatus can thus be made with great neatness and symmetry owing to the uniform heating of the glass and the fact that in spite of the softening at its centre both end portions are firmly supported and remain co-axial.

J. Sci. Instrum. 22, p. 114 (1945)
It is often necessary to hold glass tubing firmly so that it may be rotated in a glass-blowing lathe or similar device. The conventional three- or four-jaw chuck has the disadvantage of concentrating the stresses in the glass in a restricted region, and the glass is easily broken if a little too much pressure is applied in an effort to get a good grip. Wooden collets are sometimes used, but the tubing is readily broken unless it is accurately circular in cross-section and quite straight in the region gripped by the collet; commercial glass tubing often possesses neither of these properties.
The chuck described below avoids concentrated stress since the grip on the glass is obtained by wrapping steel wires tightly round it, and there is no tendency to break tubing which is bent or not quite circular in section. It can grip tubing whose diameter varies along ite length and permits quick centring of slightly bent tubes. It may be made in a small workshop, since only simple turning and drilling processes and the cutting of a ratchet are required.
A ball-race supports a tube A co-axially with the main barrel B of the chuck, and to each end-face of A three steel wires are attached by equally spaced collars C which can turn on bearings parallel to the axis of A. The other ends of the wires at the front of the chuck are attached to adjusting screws D radially mounted in the ring E which may be rotated relative to B but which is prevented from moving laterally by the flange F. The wires at the rear of A are attached to similar adjusting screws mounted on B. The radial positions of the screws are controlled by nuts G and lock-nuts H and each screw is prevented from rotating by a slot in its side which engages with a pin set in a boss on the inside of the ring E. (For the sake of clarity this detail is omitted from the figure.)
The glass tubing is inserted in the chuck as shown in the figure and the ring E is rotated so as to wrap the six steel wires round the glass. Since the ball-race allows the cylinder A to rotate freely, both front and back wires will be tightened at the same time. The ring E is prevented from turning backwards by the ratchet and spring-loaded pawl J, and the tension in the wires can thus be maintained. The glass is gripped very tightly, but with the chucks made and used we have never broken a piece of tubing, although in trying to do so a wire has been wrenched from its hard soldered junction with the adjusting screw. If necessary the grip on the glass may k, relaxed instantly by pulling out the pawl J when the ring E spring  back and releases the tension in the wires.
The chuck is not accurately self-centring but centring can be obtained quickly by a few adjustments of the screws D. Similar adjustment will centre the end of a piece of tubing which is slightly bent. We have found that in practice the setting of the rear adjusting screws may be fixed once and for all and all necessary adjustments made with the front screws.
The chuck has handled satisfactorily a range of tubing diameters of between two and three to one. The chuck described takes tubing of diameter from I in. to 11 in. Since the tubing is gripped effectively at only two places it is clear that lack of straightness does not produce any stresses in the glass, nor need the diameters at the two places gripped be the same.
The wires should be as flexible and strong as possible, and probably watch-springs would be as good or better than the stranded steel wires we have used; the greater the flexibility the greater will be the accuracy of centring.

Chemistry is our Covalent Bond
(Hive Addict)
04-10-03 02:11
No 425269
      Awesome!!  Bookmark   

Fascinating!!!  S/D is very mechanically inclined and does assembly /repair work.  He has at various times in the past pondered a glass blowing lathe.
His, ponderings, however, have always concluded that such a project would be beyond the scope of his equipment, abilities, and knowledge.  Squiddy has just seen that he was wrong on all three accounts! Thanx Lugh!!

Just curious; What type of torch set-up would one be using? Propane/oxy?  


Sometimes, I wake up Grumpy,............Other times,..I just let her sleep !
04-10-03 02:17
No 425271
      Read all about it  Bookmark   

These should answer all such questions:

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Chemistry is our Covalent Bond
(HyperLab Bee)
04-10-03 07:52
No 425331
      Russian book about glass work  Bookmark
Frist book in the list. Glass works in phisics and chem lab.
smileUseful book for me.

Good luck,
(Hive Addict)
04-11-03 01:29
No 425523
      Already got the lathe....  Bookmark   

Already have several lathes. I have an old 20" pratt and whitney metal lathe that would be perfect for converting.
Has automatic feed which would be handy for precise stretching. Only need to modify the chuck jaws or rubber coat them and make a new tailstock..

Great info lugh!! Will have to decide what would be the best way to assemble a new tail stock with my scrap lathe parts.

Yes, That pic really is me!