Member postings for RobCox

abom79 would be the first to spring to mind. It used to be a goldmine of machining tips, ended up being a product placement fest. I unsubbed after an hour long video de-rusting a chuck, pushing the rust remover. Needless to say, I fast forwarded through that video.

Some of the channels review stuff that they would have liked to buy, but were given for the princely sum of a review. If they make it clear its a review, you can always just not watch that video.

I find it simpler to do the calculations as you may not have the plate with the number of holes specified in the table.

For a 40:1 dividing head, divide 40 by the number of intervals/teeth etc you wish to machine. Reduce to an integer plus a fraction. The integer part is whole turns, the fractional part leads you to the number of holes to advance in addition.

So, for example, to do 24 teeth on a gear, 40/24 = 1 + 16/24 = 1 2/3. The plate hole circle needs to be a multiple of 3, for example, 39 is a commonly available circle, so 1 turn plus 2/3 x 39 = 1 turn and 26 holes.

You'll never need a table again.

Rob

Fine pole is better for thin work where a coarser pole spacing gives less holding power. I would expect therefore that with thicker material the fine pole may not hold the work so securely, but I have no evidence or experience to back this supposition up.

I'm with Chris Crew on this one. Speeds and feeds are fine, but you might need coolant etc for best results and if its just a hobby you can afford to back off from the industrial rates.

My mill has a lot of backlash in the table feed, so driving it too hard results in horrid noises esp with horizontal milling, so I take a cut, increase the DOC for the next pass and repeat till the mill tells me its not happy, back off a bit and I'm at the setting for a good material removal rate.

For spindle speeds, I tend to leave the horiz spindle at 100rpm and the vertical at 850 which covers most of the work I do, but I have vfd speed control so slowing it down on the fly is easy.

Hi Wade,

Dont go wasting your money on a manual. I've got 3 pdf files which I can email you. They duplicate a lot of info and dont tell you everything you want ( the table feed for example is shaft driven in the manuals, its a separate 75W motor on mine) but you might find them useful.

I put ISO220 in the horizontal gearbox, can't remember what I've pumped into the vert spindle, just NOT grease!

I'll PM you tomorrow with my email addy.

Rob

Hi Ron,

The best advice I could give would be to start on some easy to cut scrap first, ally or delrin. Do lots of practice with a standard thread size (M12?) so you've got a nut to judge when the thread is deep enough.

If you're cutting a 30mm dia thread, what's the pitch? I did a M33 x 3.5 thread on a minilathe once but it's less straightforward than plunging straight in as the large thread depth and the low power of the lathe are somewhat at odds with each other.

You might consider some thread wires to check the thread, so you know when its right or how much needs to come off, once you're comfortable with the screwcutting process. Again, practice makes perfect here too, even though theyre fiddly to use at first.

Good luck with it, Rob

I order Neatcut oil from Westway Lubricants via ebay. I'm on my 2nd 5 litre can, so I must be happy with it.

Hi Martin,

Yes, my notes were being written on the fly as I was doing the measurements, so they're not exactly, er, comprehensible. Being of a certain age I tend to be fluent in both metric and imperial and have few qualms about using the most convenient units for the measurement at hand, hence the weird dimension.

I was comparing the thickness of the gib with a selection of imperial gauge blocks, using a metric DTI. As the DTI was being used as a comparator it shouldn't have influenced what I wrote down, but for the thickest part of the gib the DTI wasn't zeroed but read +0.01mm. Had I selected some of the "tenths" gauge blocks I expect I could have zeroed it but if I had dropped the gauge block stack by 1 thou the DTI would have read -0.015mm.

So, a gauge block stack of 0.4410in was 0.01mm too tall, hence the notation. The value in the text in the posting above is correct, to the nearest half a thou, ie. 0.4405in.

When you make the gib I'd be interested in your fixturing as I could do with a new cross-slide gib on my lathe and one day may get round to making one!

It turned out a while was a couple of days! Still, here are some pics of the measurement technique and the figures.

Here's the gib coming out. Not sure if you've got the screw or not so I've measured that too:

After a cleanup, here is the item in question on the surface plate:

A fair bit of wear on mine. Also, it's not straight, which complicated the measurement procedure as I had to press it flat against the surface plate to get a consistent measurement. Firstly, length (all measurements are imperial as my gauge blocks are imperial, as is most of my workshop... and this mill):

Neither end is particularly square so about 18" is as good as it gets. There are a couple of drill holes in mine. Leftovers from fabrication perhaps:

First hole is 0.5" from the thick end, second is 9" in. I don't think they do anything.

Width of the flat bearing surfaces was gauged with a vernier. The bevels dont rub on anything so I don't think this dimension has to be accurate to the thou. Both sides are 0.80":

For the crucial measurement of the taper, I blued up 3 areas each 6" apart, lightly scribed some lines in the blue spaced as accurately as I could judge off a ruler 6" apart. These are the three measurement positions. Pressing down hard on the gib to make sure it was in firm contact with the surface plate, I zeroed a DTI with a few thou of preload. Once I had a consistent reading at the scribe line, I found the thickness of gauge blocks to also zero the DTI:

Readings were 0.4405" about 1 inch from the thick end, 0.3670" at 6" further on, and 0.2940" at 12". I make that between 0.146"/ft and 0.147"/ft taper. If you're making one I'd make it a few thou thick and scrape it in to fit anyway.

The top and bottom edges of the gib are anything but flat, so precision just isn't possible here:

Above it's clamped to a 123 block, there's contact at the first and second measurement lines, and a 12 thou gap at the third:

So to measure the broad width taper I sandwiched it between two 123 blocks and did the best I could with the callipers:

At the three measurement lines the widths were 1.158", 1.107" and 1.044". Prob about 100thou per foot allowing for the 12 thou out of flatness of the bottom edge.

In cross section the two bevelled sides are 45degree bevels:

And finally, a pic of my notebook page, with the gib adjustment screw dimensions too:

Edited By RobCox on 09/04/2023 12:06:55

Give me a while and I'll pop the gib out of mine and measure it.

Rob

Its what I do on my Omnimill to release tapers from the quill, not that I change tooling that often. I always lock the quill and the smack with a plastic faced hammer is always good and hard - no tap tapping.

I agree with what's been suggested, but I would add it looks like it's designed to fit a lathe toolpost and hold a gear blank above the spindle height so a gear cutter can be held in the spindle. The part projecting down under the two hex headed bolts at the top looks toolholder sized.

The latest dealings I had with them were unc and a unf spiral flute taps, ordered 3pm, delivered in the post 10am next day!

Thought the reply was very amusing. Showed it to my wife....

tumbleweed

Thats what I did. The project that made me realise I wanted a bigger lathe was when I was tarting up a spindexer which had poorly machined ends on the bore. There was - literally - 1mm of clearance over the bed.

So I ended up with an M300, but the minilathe was used to machine replacement shafts for the Harrison. I still cant bring myself to part with it, even though its relegated to the garage and doesnt get used.

One mod that doesnt get much mention, not complicated and was the first I did, fit a plate on the back of the apron to keep chips out of the otherwise open gears.

Other mods I did were the tapered roller bearings (I was one who experienced a massive parting off improvement), tapered gibs, thrust bearings in the compound slide, a threading dial (didnt like the OEM one), cam lock on the tailstock and a qctp, though that had to wait till I'd got my first mill.

How about a Centec 2A? There's one for sale on mig-welding.co.uk for 2/3 of the cost of the 2B.

Orientation B is correct but your toolbit is sloping the wrong way. You want the face of the tool approaching the work to be angled back, akin to positive rake on the top of a lathe cutting tool, as per A. In orientation A the bolt holding the tool takes the full cutting force rather than the toolholder body.

Hi Wade,

From your description it appears to me that the table is not at 90deg to the slide on the column. You may find that the gib between the column and the knee needs adjusting which I seem to remember is a normal non tapered gib but I havent had to adjust mine in a long time so I may be wrong.

The y axis gib is tapered and is thickest at the front. Make sure the screw at the back is tight otherwise the gib may get pulled in when the table is moved towards the operator which will cause it to jam.

Rob

One more comment on the inaccuracy of that animation. Notice how the chips fall into a single pile, rather than spitting all over the workshop!

Several things to check. I assume you have a dial indicator or a dial test indicator. Mount this on the spindle so the tip describes a circle about as big a diameter as the table depth front to back. At four compass points measure the difference in table height. Any errors will cause your circular cutter motion to describe an ellipse on the part.

Second, check the head is rigid when not locked (you can use the same DI or DTI to measure how much it moves when you push/pull on the spindle) . If its not rigid, try feeding with the quill instead with the head locked.