Hold Fast Vacuum Chucking System archive
Monday 25 November 2013
Walter Hall looks at the vacuum holding system from Hold Fast and finds it to be versatile, well made and cost effective
This system, which is designed to fit any lathe with a hollow headstock spindle and a No.2 Morse taper, includes an adaptor kit consisting of a threaded tube that passes through the lathe headstock spindle, a sealed rotary bearing, which fits the outboard end of the tube, and a locking spindle adaptor, which seats into the Morse taper and against which the assembly is tightened.
The assemblyThis assembly is connected by means of a small diameter vacuum hose to a vacuum generator, which works on compressed air and must be attached to a compressor, producing a minimum of 2cfm of air at between 75 and 150 psi. The vacuum could alternatively be supplied by means of a vacuum pump. Chucks of 150mm and 75mm diameter are available to fit lathes with a 1 1/4in x 8tpi spindle thread and adaptors are available to convert these to fit 1in x 8tpi spindles. A nylon anti-lock washer is provided to fit between chuck and spindle.
In useMy first impressions on taking the system out of the box was that the aluminium-bodied rotary bearing adaptor seemed a little small and flimsy and the vacuum tube reminded me of car screen washer tubing, but my concerns were soon allayed when the system was fitted to my lathe and operating. While I cannot comment on the long-term robustness, having only used it for a short while, I can confirm that these components are certainly up to the task. The vacuum generator is a small aluminium box with a standard 1/4inbsp inlet for the compressed air, an outlet nipple for the vacuum tube, an on/off switch, a regulator valve and a vacuum gauge. Attached to my 2hpP 115psi compressor it produced vacuum which measured at around 20hg. The box, as supplied, has no means of attachment to the lathe or any other surface, but the aluminium back panel is easily removed and could be drilled for a mounting to be fitted. The vacuum adaptor kit is fitted to the lathe by passing the threaded tube, with rotary bearing adaptor already fitted, through the spindle from the outboard end. The locking spindle adaptor is then attached to the inboard end of the spindle and the assembly hand-tightened by turning the rotary bearing adaptor. Any excess tube on the inboard end must be cut back with a hacksaw so that it projects about 13mm beyond the locking spindle adaptor. This is then de-burred and tidied up with a fine file. This was all carried out fairly easily, although the provided instructions could perhaps be a little clearer. The system is then connected to the vacuum generator by means of the vacuum hose. I found the aluminium threads on the chucks to be a little rough and they needed a spray of PTFE lubricant in order for them to screw easily onto my lathe spindle.
Further testsWhile vacuum chucking systems are primarily designed to allow reverse chucking for the removal of chuck mountings and the finishing of bases etc., I gave the system a thorough workout by mounting a 200mm x 80mm imbuia (Ocotea porosa) blank and taking some fairly heavy cuts with a 13mm bowl gouge. In normal use I would provide support for such cuts with the tailstock but even without the benefit of support the blank held firm on the chuck with no movement. I also mounted a smaller square of sycamore (Acer pseudoplatanus) to see if the additional forces generated by the irregular cutting action would dislodge the work but found the corners could be turned off without any dislocation of the work.
It is of course possible to dislodge a workpiece from the chuck, but when I took the system to get a second opinion from my friends Bob Chapman and Neil Lawton, we found it was only really possible to do this by deliberately initiating a catch or taking an unrealistically heavy cut.
If used with a compressor with an air storage tank rather than direct feed, the system is safe in the event of power failure as the residual pressure in the tank will maintain the vacuum for some time. The on/off switch on the vacuum generator will, however, turn off the vacuum immediately and should, on no account, be turned off while the system is in use.