My drill a Sealey GDM30A has developed an unacceptable run out. Measuring this with the dial gauge suggests it's as much as 0.2 mm which is far too high and the drill really can't be used like this. Removing the chuck and checking the tapers showed that most of this run out was due to wear and damage inside the chuck taper itself. Simply replacing the chuck should therefore fix the problem. Unfortunately this particular drill has a Jacobs 21/2 taper on the spindle, requiring a Jacobs 2.5 chuck and manufacture of these ceased some 70 years ago- spares haven't been available since the 60's.
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| Date plate on my existing drill- yes it really is a 21/2JT chuck fitting even though many suppliers have never heard of it and assumed I didn't know what I was talking about!. |
There are a few possible solutions to this problem- from quick and dirty to thorough and involved! The modern version of this drill is the SDM30 by Sealey which is fitted with a B16 taper compatible with many modern chucks. It seemed to me the most effective solution would be to replace the spindle with the B16 spindle from that model.
Having contacted the Sealey Technical advice line it seemed that the swap would be straight forward and the replacement spindle readily obtained. I therefore purchased the new Sealey spindle and set about dismantling the drill (see below) in order to commence the rebuild. Unfortunately this advice turned out to be incorrect and there were complications yet to arise.
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| New spindle from Sealey with 2MT chuck attachment. |
The main problem with this approach was that I had intended to simply replace the spindle, reusing the existing upper spindle sleeve so that the pulley block and its mounting would be unaffected. Sadly, the new spindle will not fit into my existing GDM30A upper spindle sleeve because the new spindle has a square drive section and the original a hexagonal. You can see this in the pictures of the dismantled components below.
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| Looking inside the existing spindle sleeve and the spindle drive profile- GDM30a drill |
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| Square drive section from the SDM30 drill spindle will not fit inside the GDM30 spindle sleeve. |
However the new spindle from the SDM30 has a squared drive which will not fit inside the upper spindle sleeve from my old drill. I will therefore need a new spindle sleeve and its bearing mounting systems as well. Sadly it gets worse because the new spindle sleeve has a different pulley block attachment; instead of the taper used by the GDM30a, the new sleeve is cylindrical and mounts the pulley block using a grub screw- I need therefore to either replace the pulley block (new blocks are aluminium) or bore out the old one removing the taper and fix it to the new spindle sleeve with a grub screw. Although this is irritating new parts were on special offer and relatively cheap so I tried both approaches. Overall the modifications should be well worth it to obtain a more modern drill.
As mentioned above, I had already dismantled the drill ( see below) and so for all this time I had been without a drill and therefore I had to consider other, less satisfactory solutions. Since the existing spindle wasn't bent it should be possible to use it provided I could find some way of mounting a new chuck firmly and true to rotation.
Taper adjustment
A little research showed that the obsolete JT2½ dimensions are quite close to the more modern 6MT. I can obtain a 16mm 6MT keyed chuck fairly cheaply. I found that this would mate with the spindle taper without modification but the fit wasn't great-the spindle would only penetrate about half way into the chuck and much of the taper surface was not engaged. Short of having the taper reground commercially, the only course open to me was to grind the new chuck onto the spindle to improve its fit. I was able to hold the spindle in the lathe chuck whilst mounting the new drill chuck backwards in my tap holder- which was itself mounted in the tailstock. To do this I used a piece of straight round steel bar gripped in the chuck of my tapping unit. I could then grip this in turn with the jaws of the new chuck jaws so that its taper now faced forwards, towards the spindle held in the lathe chuck.
There was quite lot of grinding required so I used both coarse and fine valve lapping compound in turn- smearing the spindle taper with the appropriate compound and then advancing the tailstock so that the tapers engaged. I rotated the lathe firstly by hand and then at low speed whilst holding the tapping unit to prevent rotation. I ground in both directions by reversing the lathe. Clearly not the best solution in terms of accuracy but an awful lot better than free hand grinding. After grinding the fit was greatly improved but not perfect. I wont be able to check whether runout has been improved until I've reassembled the drill.
Spindle tapping
The second possibility, assuming that my grinding proves out of true or attachment is simply insecure, is to convert the drill to use a threaded chuck by drilling and tapping the end of the spindle. I can then use a short threaded stud as an adapter and screw the new chuck onto that. I decided to do this at the same time as grinding the taper since both required holding the spindle in the lathe. I didn't want to weaken the end of the spindle too much so chose to use a 3/8 threaded chuck rather than a half-inch. I found a 13mm chuck with an internal 3/8 thread (24tpi UNF) from Chronos tools and UNF studding was available from Ebay. This required an 8.5mm pilot hole to be drilled in the spindle which I did in the lathe to try and keep it true to centre.
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| Drilling the spindle end- note the taper has been ground at this stage but not yet polished. |
To my surprise the spindle drilled quite easily as whatever hardening process had made the grinding difficult didn't seem to have affected the metal of the interior. I could then thread the inside of this bore using an HSS tap set, moving to the plug tap to get as close to the bottom of the bore as possible.
Finally as as a temporary measure I reassembled the drill using the reverse of the process below. Having attached the 6MT chuck I found rotation was now smooth with run-out vastly improved. Drill functionality restored- at least temporarily whilst I await delivery of the new parts.
Dismantling the drill
This is pretty much a reworking of my first post in this blog although I tended to use a more direct approach to pressing and removing the bearings.
1st step as always was to remove the drive belts and Unscrew the nut holding the drive pulley block to the spindle which is a left hand thread . I then removed the 4 screws that hold the drive belt case at to the top of the drill removing the case as well as the pulley block.
I have replaced the screws in the top of the drill for safekeeping.
Next I removed the nuts holding the rise and fall sleeve spring mechanism to the left hand side of the drill.
The spiral spring simply pulls off inside its case its not under much tension
Having removed the Spring the rise and fall sleeve rack and pinion mechanism could be removed by simply pulling handle out to the right.
Next remove the depth stop guide by unscrewing the nut at the bottom and simply pulling the threaded shaft out
Loosen the sleeve slide adjuster grub screw having 1st loosened the lock nut
Remove the upper spindle sleeve clamp grub screw at the top of the drill on the left.
The spindle and lower sleeve can then be removed by tapping downwards using a soft drift on the top of the spindle inside the upper spindle sleeve
This removes the spindle inside the rise and fall sleeve.
Here you can see that the E clip I placed on top of the upper bearing in the sleeve is still present
Remove the E clip and then you can tap the spindle downwards out of the rise and fall sleeve. The lower bearing comes out attached to the spindle the upper bearing remains inside the sleeve
To remove the lower bearing insert a screwdriver and twist to force the inner race away from the taper base of the spindle.
The lower bearing will then slide most of the way along the spindle until it reaches the top bearing land. Rest the bearing in the jaws of a vise and tap the rest of the spindle through to remove it completely.
Changing the spindle
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| New spindle from Sealey with 2MT chuck attachment. |
To start reassembling locate the bearing and tap it down over the new spindle to the lower bearing mounting land. I used a hollow steel tube that slipped over the spindle and rested on the bearing inner race to do this
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| New sleeve with lower bearing fitted. The hollow tube used to install it is shown above. |
The new spindle could then slip easily up inside the rise and fall sleeve and through the top bearing.
The first difference is that although a "retaining ring" is shown above the top spindle bearing (where the E clip was fitted in the old drill), there is no groove in this new spindle to accept a circlip and so fix it in this position. I fitted a star washer at this point, tapping it down the shaft to contact the bearing.
Sadly this left an unacceptably large amount of wobble in the shaft. Inspection showed that the ground bearing land on the new shaft is lower than on the original. Unfortunately the recess in the feed sleeve isnt deep enough to allow the bearing to sit this low so it was actually resting above the ground land and was consequently too loose on the shaft. To overcome this I was forced to deepen (extend the bore) inside the feeder tube so that the bearing could sit lower.
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| Bearing location groove inside feeder sleeve. This needs to be extended by 10mm so that the bearing sits further inside the sleeve. |
When the bearing is positioned here then the groove in the spindle can be used to fit a circlip.
You can also buy a new feeder sleeve from Sealey but if you do, insist on a cast iron one as the more modern replacements are aluminium and a poor fit in the drill body.
Further, although the upper spindle sleeve bearings are the same in both drills, the mounting methods are different. The older drill GDM30 uses two bearings separated by a plastic spacer, the newer drill uses circlips to separate and locate the bearings: circlips which presumably locate in grooves formed inside the drill body. Since my drill body is the original GDM30 version I don't have any such grooves, and in any event the clips needed are not available without a long lead time. I'm hoping to reuse the "twin bearing and spacer" system which fixes and positions the bearings using a grub screw to secure the intermediate plastic spacer. I therefore retrieved the plastic spacer from the old upper spindle sleeve.
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| Plastic spacer from the older drill which I hope to reuse with the new spindle sleeve (when it arrives!). |
In fact the plastic sleeve turned out to be too thick for the new spindle so I machined a narrower soft aluminium spacer of similar dimensions and that worked well. It allows some adjustment of the depth to which the spindle sleeve is inserted so as to keep the pulley blocks level.
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| Thin aluminium spacer inserted between bearings on spindle sleeve |
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| Spindle sleeve secured at aluminium washer level by grub-screw |
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| Pulley block height adjusted (new pulley block illustrated) |
