Thread: Macson Bench Surface Grinder Rebuild

Originally Posted by CGroves

Stuart: I think what I've done is probably overkill but it was a good exercise. I hadn't played with helical thread milling before. The male thread I machined like the female one with a 60deg equal angle cutter going around the outside.

Nothing wrong with a little overkill now and then. My table is 60Dia x 3.6mm and 50SQ x 3mm, with M32x1mm thread. Last thread question promise, did you go full depth in one pass? Great work.

Yes forget my gasket theory in this case

Stuart

Stuart,

Hopefully not the last question, questions are what make the threads interesting )

Agree nothing wrong with a little over engineering. I would have gone for the three leg setup like your stand but i'll get around to putting some drawers in the stand to make use of the space. I also made the stand so that the surface plate will overhang by 5mm on all sides. I thought it may come in handy if I ever have to scrape or measure the inside faces of something "L" shaped.

Below is a diagram of the cutting path.
Attachment 215293

It was two passes the last one was a finish pass at 0.1mm. 19.5mm DIA cutter, Initial pass: 775 RPM, feed rate 243mm/min.

Christian

Originally Posted by CGroves

The other mystery is that there was no gasket on the grinding wheel end only on the pulley end. I would have thought there would be one on both ends? I'll need to make up a couple of new ones. Its 0.3mm thick however I'm not sure what the material is, however when teared it does have a fibrous structure. So I was thinking of using 0.4mm gasket paper as a replacement. Does anyone else have other recommendations?



Christian

Hi CGroves, All looking good, coming along nicely.
Regarding a gasket at the duplex bearing end, if it's the set up I think it is then it's probable that there was no gasket on that end. If you put a gasket in you may not be allowing the spigot on the end plate to push the outer races of the bearings together thus effecting the correct preload and also holding hold them tight in the housing. Usually there is actually a small air gap between the housing end and the flange of the end cap thus ensuring that the bearings are being clamped by the spigot, one can use a soft compressible gasket "goo" or some such to take up the air gap.

Cheers.

The motor is the last piece of the surface grinder to be disassembled. I

The motor plate says:
Mc Coll Electric Works Ltd.
Refer No. 35409 XD316
F.R. 3524 Type 0ZX31
RPM 2850 0.5 HP 3PH 400V

Here's a couple of pictures of it in pieces, not exactly pristine.
Attachment 215451 Attachment 215452

It looks like the fan side bearing has been replaced at some stage. As it has a metal side and other side open (the pulley end is completely open). The fan bearing is also a newer bearing. The pulley side bearing is not real good. I can only assume whoever previous changed the bearing couldn't remove the pulley to get to the bearing on that side. The bearings are numbered 6202.

Here's the connection block. I assume from the connectors that I won't be getting away with getting it reconfigured to 240volts
Attachment 215453

As I mentioned the surface grinder is now completely disassembled. Most of the components have been degreased and cleaned up. Now to see about getting the paint removed so that I can respray it. My current plan is it to get it sand blasted off, although I'm yet to investigate that.

Christian

OK, Christian, that motor won't be much of a problem. And if it is, I will happily give a 1/2hp 3-phase replacement motor (I have several, but can't recall if any of them are 2800rpm.
Firstly, you will need to thoroughly clean the coils and wiring. Do NOT use any solvents. Used compressed air in the first place, using paint brushes to move most of the dust and crud. There are special motor cleaner liquids but I haven't seen any for a while. I would try 'oil and wax remover' that spray painters use. I don't believe it's a solvent - others here may know better. A cheap degreaser may be OK too.
The 6202 bearings are cheap off the shelf bearings - you can afford to buy brand name ones and don't use a hammer to mount them on the shaft - press them on. Same with the motor end shields when you reassemble: don't hit anything with a hammer.

Incidentally, the play you felt in the spindle bearings: they are angular bearing which are ALWAYS 'loose' until they are fitted in pairs and loaded in the direction of their angular contact. When you mentioned that they had some play, was that on the spindle, still installed or seperately in your hand?

The reconfiguration of your motor for 240V is fine. I'll post a photo shortly with some explanations for you. It is currently wired in 'star' shape and needs to be wired in 'delta' shape. So there is a 'star point' connecting the three sets of windings together - the other ends of the coils which are not connected to the terminal block.
Whoever changes this - maybe you - brings three new wires out into the terminal box - probably through the same holes of the current wires - and connects them to the three wires in the box into the same terminals.
Joe

Here is a picture of your motor stator with an indication of what's going on.

The following is a description of what a motor rewinder will do - and I have done several times. It is NOT an instruction to anyone not familiar with the hazards of electric motor windings.
If anyone attempts this on their own motors, they take full responsibility for their own actions! The work itself is not dangerous, but if mistakes are made, the insulation could deteriorate or be damaged and make the motor and/or the machine it is attached to fatally dangerous once in use - even much later on!

After everything is cleaned, one will have to look very closely at the spagetti tubes I indicated in white and see how many wires go into them at each end. It looks to me that one or two of them near the top of the picture have wires going in at just one end - an idication of a likely junction point.
When one finds the one that has 3 wires going in - possibly two from one end and one from the other - very gently slice open the spagetti tubing. Once the wires inside are visible, and it can be confirmed that there are 3 wires twisted and soldered together, they can then be freed completely - maybe by trimming off some of the string bindings - without scratching the lacquer of any adjacent wires. These three wires are then lifted clear of the coil and either unsoldered while untwisting, or - if enough wire can be freed of each - the twisted bit can be cut off.
Next one needs to solder 3 new flexible insulated wires (preferably nice soft silicone insulated flex) onto the now separate and free ends. These flexible wires only need to be around 1mm2 or less cross section - quite thin - because each doesn't carry much current all in a 1/2hp motor.
The next step is routing these three wires - safe from possible contact with the spinning rotor, once reassembled - back to the terminal block.

Slide some new spagetti tubing over these joints to insulate them, bend the coil wired back tight to the coils and fix them there with epoxy adhesive - e.g. 5 minute Araldite or better. Since epoxy doesn't actually stick to silicone and some other insulation, it needs to encapsulate the whole wire to hild it in place one cured. Epoxy is also a good insulator for the soldered joints, the spagetti tubing covering it can be sealed with it at both ends.

Each of the new wires needs to be identified to be the 'mate' to one of the original wires in the terminal box with a multimeter.
The new wire connected to the coil wired to terminal 1 should be pulled through the hole adjacent to teminal 2, the new wire 'mate' of terminal 2 is pulled through to terminal 3 and that mating with terminal 3 pulled through the whole next to terminal 1.
By then connecting the 3 new wires to their nearest terminals, the delta configuration is completed.
At every construction step along the way, a check should be done to confirm that NONE of the coils have any continuity with each other or the motor frame. There should be NO continuity between any coils until the final connections in the terminal block are made - when all three coils are connected to each other.

Hope that explains the process and allows members to ask intelligent questions off a rewinder - or the knowledgable adventurers amongst us to do it ourselves.

Joe

Hello Log,

I was having trouble getting my head around exactly how the spindle head is put together. So I decided to measure it. Below is a section view of the spindle head assembly:
Attachment 215547

It seems you're right about the air gap. Based on the measurements once its all assembled there will be an air gap ~1.3mm. The end caps are slightly different the wheel end cap loading the bearing outer rim and the pulley end cap loading the bearing in ring.

I still don't understand why the end caps have a curved groove on them (indicated by the ???). I also don't understand how the oil is going to stay in the spindle head. Its not exactly a tight fight between the end caps and the spigot and the bearings aren't sealed.

Thanks, Christian

I wonder if your grinder is supposed to have an oil drip feeder on top where you currently have an oil cup, like in this picture from a 1949 catalogue.. it would be a total loss oil system design.... Also those bearings are not thrust bearings, they are angular contact bearings.. Also the bearing on the other end is a precision bearing as well, I think I can see the high spot mark on the outer race in the picture... It looks like an arrow, the same mark is on the two angular contact bearings.. Fafnir number for a 6205 precision bearing is MM205, if you wish to search for one..... My Macson Tool and cutter grinder has the similar spindle bearings in it as your surface grinder uses (they are a bit bigger).... I got precision bearings from US ebay for it... They were not cheap, but a lot lot cheaper then I expect they would have cost here...

Hello Joe,

Thanks for the detailed information on the motor. Glad to know there's a possibility, although its not as simple as changing the bridges between the leads. Given the possibility of stuffing up the coils and that its not exactly an item that easily replaced with like I think i'll be taking it to a motor rewinder.

With respect to movement in the thrust bearings I don't know to quantify the movement but a new bearing whilst having some play in still feels "tight" the existing bearings felt really loose. Even when on the spindle with the spigot installed there was some play.

I don't believe in cheapo bearings so i'll be putting in decent ones and will be avoiding the use of a hammer. When I was at high school I used to work at a place recycling plastics pulling apart shrink wrap bales to feed onto a conveyor belt. One of the fitters would take pity on me and take me to help him. One day he asked me to remove a motor flange and left me to my own devices... my tool of choice a "hammer". Didn't know what a gear puller was. Needless to say the reaction of the fitter to "hammer finished" flange has meant to this day the hammer sits safely in the tool box for these sorts of operations

Christian

Originally Posted by CGroves

Hello Log,

I was having trouble getting my head around exactly how the spindle head is put together. So I decided to measure it. Below is a section view of the spindle head assembly:
Attachment 215547

It seems you're right about the air gap. Based on the measurements once its all assembled there will be an air gap ~1.3mm. The end caps are slightly different the wheel end cap loading the bearing outer rim and the pulley end cap loading the bearing in ring.

I still don't understand why the end caps have a curved groove on them (indicated by the ???). I also don't understand how the oil is going to stay in the spindle head. Its not exactly a tight fight between the end caps and the spigot and the bearings aren't sealed.

Thanks, Christian

Hi, Regarding the wear marking on the pulley end end cap as shown in earlier pics this is probably because the "spigot", as you have called it has been loose at some stage and allowed the bearing inner ring to rub against that section of the end cap. You won't need to remove that damage just dress off any burrs. The bearing is clamped on the shaft by the spigot(as you said) and as the shaft expands lengthwise the outer race of the bearing can slide in the housing.

Regarding oil; from your earliest pics it appears(?) that the oil sight glass level line is lower than centre line of the shaft, the line is maybe/possibly in alignment with the lowest periphery of the shaft, if this is so then you should not lose oil when the spindle is stationary and during running you will lose oil slowly. As pointed out by .RC. there was originally an oil drip feeder, maybe that is what was on yours before the flip lid oiler that is now on yours(as per earlier pics).

Cheers.

Originally Posted by Log

As pointed out by .RC. there was originally an oil drip feeder, maybe that is what was on yours before the flip lid oiler that is now on yours(as per earlier pics).

Cheers.

I was just looking at the spindle photo's and I see there is what looks like an oil sight glass on the side of the spindle casting.. Probably designed to leak oil slowly and you top it up every day....

Originally Posted by CGroves

Snip

With respect to movement in the thrust bearings I don't know to quantify the movement but a new bearing whilst having some play in still feels "tight" the existing bearings felt really loose. Even when on the spindle with the spigot installed there was some play.

Snip

Christian

The angular contact bearings when assembled won't have any play, they will have preload, that preload is built into the assembled pair, both the outer races and the inner races are clamped tight together and the built in preload will be there.

Cheers.

Hello Rc,

Sorry about the terminology... the bearings have "thrust" on them so that's what I was using.

I've got a 1955 catalogue and it doesn't show the oil drip feeder. I've got pictures of other Macson bench surface grinders that show the same oil cup that I have. The spindle housing also has a sight glass in it.

Although I think I know how the oil stays in, geometry. Oil level lines in the sight glass are fairly narrowly space. Measuring the height of the lines, the top line corresponds to exactly the same height as the inner diameter of the end caps.... So maybe this circular groove is catching oil thrown to the top when the spindle is turning and returning it to the bottom? If one looks closely the groove isn't entirely circular there's an angle on the outside of it. So the top half would collect oil and the bottom part would allow the oil to flow out. Clever designer....

Christian

I liked the look of your grinder so much i went out and got one, well sort of

i have a 3A Hercus tool and cutter grinder i got a while ago, surface grinding was what i was after and it seemed a bonus that i could allso do cylindrical grinding etc it came with a magnetic chuck but sadly the vertical feed is way to course to do a good job as a surface grinder

So when the macson showed up i grabed it, but allas its missing the counter balance springs and mech, could you include some pics and some dimension so i can chase up some springs and sort it out, i gather the springs are anchored in the base with the cross pin (missing on mine) dont know if the pully is there will try to see during the week, whats at the top of the springs ? had any luck with a manual ? what are you going to use for spindle oil ? Vactra 2 for the ways ?

yep another machine, might sell the Hercus see how i go

Cheers
Fred

Hello Fred,

Any chance of you posting a photo of the grinder? It would be good to see how it compares to the one I have. I now know of 10 grinders. There seems to be a couple of design variations.

Unfortunately I haven't been able to find a manual. I've contacted the Melbourne model engineers society and found another owner but no manual. I've managed also to track down two Macson ex-employees. One is still checking with his contacts, fingers crossed he comes up with something.

In terms of oil, the for slideways I'm intending on using a Vactra 2 or equivalent. For the spindle I haven't worked that out yet. I'm open to suggestions on this one.

With regards to the spring balance mechanism, I've attached a PDF that should have all the details you need. I didn't include anything on the wheel. Let me know if you need that.
Attachment 217645

Christian