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| RussellT:
Here is yet another mini mill modification thread. I don’t expect it to be the best or even original but I hope it may interest a few people. I bought the mill from another madmodder :beer: a few months ago. None of what follows is a criticism of him in any way. I have been slow at getting to grips with the mill. Other tasks and burning out the motor :zap: have caused some delays so my first modification after replacing the motor (using the money I had planned to spend on a milling vice) was to add a cooling fan. There was plenty of space under the motor cover for a fan and some hunting in a box of old fans produced a circular fan that sat nicely on top of the motor. It needed 12V DC. The mill already has a built in 12V lamp which runs off a 12V electronic transformer. I decided not to rectify the AC at the transformer as the diode voltage drop would make the light dimmer, so I used a rectifier that would sit on top of the fan motor and wired it in to the lamp 12V AC. I needed to add a capacitor to smooth the rectified AC. The value was chosen by increasing the size until there was no improvement in the fan’s performance. The fan was secured to the top of the motor with a bead of silicon sealant. The rectifier was secured to the fan in the same way. I considered adding some more cooling slots to the motor cover. There are already some in the back, but decided to wait and see how much difference the improved airflow made. I also reduced the fuse rating in an effort to protect the new motor. The new one hasn’t blown yet so I may reduce it some more. An occasional blown fuse is a trivial amount of cost and effort compared to a replacement motor. Russell |
| John Rudd:
Russ, Good idea using the 12v feed from the lamp to power the fan......but, if it is 12 v ac or more, your capacitor is not long for this world..... 12*1.414 gives a peak voltage of nearly 17vdc.....not good for a 16 v cap.....you may want to consider changing it..before the cap expires and it starts snowing..... :zap: |
| RussellT:
Hi John You're quite right. I had overlooked the RMS factor. However if I push the margins to the limits there are two diodes in the circuit at any one time so presumably the peak voltage would be 1.4 volts less. Or is that just bad practice? Russell |
| RussellT:
Well I don't think it's good practice so I changed it. I had a 50V one salvaged from something I threw away, and although slightly larger it still fits under the cover OK. Thank you John for pointing it out. Russell |
| RussellT:
When I bought the mill it had the inexpensive digital readouts from Arc Euro Trade on the Y and Z axes. I decided I would like one on the X axis. However as I’m a cheapskate I decided to take the Z axis readout off and use it on the X axis. Then I could buy a shorter (aka cheaper) one for the Z axis. I looked at lots of other installations on the internet. To my surprise lots of them put DROs on the back of the table. I decided that it had to go on the front because it would reduce table travel if it were on the back – although arguably installation was easier. Buying a mill with extra table travel is expensive so it seemed better not to restrict it. Here’s a picture of the original arrangement. Table stops slide in the groove on the front of the table and are supposed to stop the table when the stop contacts the pointer in the centre. Actually they just push the pointer to left or right before stopping the table so I decided that removing them would be no great loss. That meant that I could use the table groove for mounting the DRO scale. The next issue was how to mount the reading box. Clearly it has to attach to the base of the table slide but offering it up shows that it won’t fit between the X axis clamp screws. I thought about several options. I considered filing away a bit of the plastic box, or only using one of the clamps. While I thought about it I put some grubscrews in the clamp holes so I could carry on with the rest of the fitting. I realised that I could still turn the grub screws with an allen key even when the read head was in place. So I made some special screws for the clamps. Here’s a picture of a new one next to an old one. I carefully made the new ones the same length as each other, only to find that the blocks at the bottom of the hole which bear on the gib strip were different sizes, so I made a small spacer to go under one of the screws. The clamps to hold the scale to the table were more complicated than I expected. I made them with a raised portion to fit the table groove so that they would line up with the table. I had to cut away some extra metal on the back to clear the rivets holding the measuring scale to the front of the table, and I also had to cut away some more so that they didn’t foul the base of the slide. After all my efforts to make these identical I discovered that the groove in the front of the table wasn’t parallel to the top of the table so I modified the clamp at the low end by opening out the slot for the scale and adding a grub screw so that the scale could be adjusted parallel to the top (and travel) of the table. A piece of scrap was cut to fit the back of the read head. The screw mounting holes were chosen so that the screw heads would fit in the groove in the table. A washer was used behind the plate to avoid any twisting effect on the scale or read head and it was fastened using one of the original scale pointer holes and screws. Here’s a picture of the installation so far. I plan to add a guard at the front of the table to keep chips away from the scale, so I’ll come back to that later. Russell |
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