Here is a list of all the postings Douglas Johnston has made in our forums. Click on a thread name to jump to the thread.
|Thread: pcb guillotine blades|
The scoring idea sounds interesting, I must give it a try .I suppose a stanley knife might even be worth a try.
I see what you mean about the attack angle reducing with a straight upper blade if the upper blade is pivoted at one end. In my design the upper blade is held at a fixed angle and is guided vertically (as in the head chopping guillotine the French were so fond of) so the attack angle stays the same throughout the cut.
I hope somebody can provide me with the attack angle used on commercial guillotines.
A few months ago I made a guillotine for cutting fibreglass pcb boards, based on a commercial design I saw pictures of on the web. It consists of a straight blade at a shallow angle cutting against a bottom fixed blade. I was delighted when I tested it on a sheet of paper and obtained a perfect clean cut.
When I tried it out on a piece of pcb material, things went downhill rapidly, the force needed to cut the board was much too high causing all sorts of problems. When I made the guillotine I made an attempt to measure the slicing angle between the two blades from a picture I printed out, but realised this was a bit suspect.
If anyone has access to a pcb guillotine (or even a sheet metal one) I would love to know what angle they use beween the two blades as I suspect I made the angle too shallow in my design.
|Thread: Demagnetizing digital caliper?|
An old ac motor with the rotor removed works well as a demagnetizer. Don't plug it into the mains, which would overload it, but connect the field winding to a 12/24V ac supply from a transformer.
|Thread: Lathe tool insert bits|
A number of people seem to have the mindset that carbide tips are no good for smaller lathes and are only good for deep cuts at high speed. This may well have been the case when carbide tips first came to be used in the home workshop, but things have moved on since then.
Old stock bought on fleabay may prove to be disappointing but there are excellent tips out there that have good positive rake and sharp edges and will perform very well on a smaller lathe. I use a Myford Speed 10 lathe (a baby Myford) and get excellent results with decent carbide tips even with finishing cuts. If you look at the edges of a good quality solid carbide endmill you will notice that the carbide can be very sharp and this sharpness is obtainable on a carbide insert for lathe work. The downside is that you have to be careful not to chip the edges which are quite vulnerable.
|Thread: Quorn or Vertex cutter grinder ?|
Thanks for your reply David, I will give a diamond wheel a try and see how it performs.
The Arc diamond wheels look very nice, can you advise me on the following points:-
(1) Do you use them for HSS as well as carbide as I have seen people saying not to use them on HSS.
(2 ) Do the diamond wheels need dressing like the stone ones and if so what is used for this.
(3) Do they give a better surface finish than the normal medium (60 grit) stone wheels.
I have just been sharpening some endmills on a Quorn that I have just finished building (bought the castings 20 years ago!) and it does the job very well ,but would I do it again?, I don't think so. I'm not saying it takes 20 years to build, many other things got in the way in between long spells when no work was done on it, but there is a fair amount of work involved.
If I was starting now I would probably build a simpler design which is all you need for drills and endmills and get a working machine in a reasonable time. Quorns do crop up on fleabay but I would be very wary of buying one unseen since build quality is important if the machine is to work well.
I have been using grindstones I bought with the castings but notice diamond wheels are now available. Are diamond wheels good for the likes of a Quorn?
|Thread: Please assist with my fist mill choice|
I think I spoke too soon Derek, I have just been out to my workshop and found the temperature was 1 degree C. Quickly closed the door and came back inside the house. Clearly not as hardy as I thought!
Now now magpie, we in Scotland are hardy types who never feel the cold.
|Thread: Drilling sliding scales|
I did this a while ago and found that a HSS drill was no good. I ended up using a solid carbide drill and this proved to be ideal. You could use a clamp type fixing which would eliminate the need to drill the scale.
|Thread: Myford Super 7|
With current income and 1970 prices life would truly be pleasant. We can only dream.
|Thread: How Britain Worked|
Enjoyed the first episode very much but did need a babel fish in my ear to pick up all the dialogue.
|Thread: diamond needle files|
Just been to my local (UK) Aldi shop and picked up a set of 10 diamond needle files for a fiver. Nice neat size and look a decent quality (for Aldi! ) .Be quick if you are interested as these tend to go fast.
|Thread: Announcement from Arc Euro Trade Ltd.|
Living in Scotland the major exhibitions are too far to travel and I have to rely on the mail order companies for equipment. Over the years the standard of service from these companies has improved considerably. I can remember waiting weeks for orders to arrive in the past, whereas delivery now is often next working day.
Just a little plug for Arc Euro, I ordered some items yesterday from them and shortly after received an email telling me I will get them on Monday (next working day) and will be given a 1 hour delivery time slot on Monday morning. Thats what I call impressive service (free carriage as well having spent over £60). Well done, that's all I can say.
|Thread: Choiceof DRO|
It is not a matter of working to an accuracy of 1 micron, the 1 micron resolution simply makes it easier to get a decent accuracy. Remember resolution and accuracy are two different things.
I've uploaded five pictures of the DRO into an album.
Hi Maurice, the magnetic sensor is only approx. 5cm long, 1cm wide and 1.7cm high and fits onto an L shaped bracket fixed to the back of the cross slide base. I had to machine a flat area on the base to achieve this. I have a long cross slide on the lathe and I extended this by another 5cm with a block of aluminium bolted to the end, then machined a 1cm wide area about 1mm deep along the underside of the slide and aluminium block, into which the magnetic tape was located using superglue. A thin non magnetic metal plate was fitted over the magnetic strip to protect it from any machining oil or debris.
Careful alignment was needed to achieve the right gap between the magnetic tape and sensor and to avoid conflict with the cross slide screw. The cable from the sensor was routed under the lathe bed and connected to the same digital readout used for the mill. I made a switchover box so that I could select the output from either the mill Z axis or the lathe cross slide sensor.
If anyone is interested I can take some pictures and post them if I can work out how to do it.
I have just fitted a 1 micron magnetic scale to the cross slide of a Myford Speed 10, fitting the scale under the slide to keep it out of the way. I was always put off fitting a scale down the side of the slide because it would get in the way of things, but this way works a treat. It is a bit more work to do it this way but well worthwhile. The only downside would be a clash with a rear mounted taper turning attachment (as well as the cost -these magnetic scales are not cheap but you soon forget the expense)
|Thread: Cutting oil|
Yes very strange that the broaching oil appears in the latest catalogue but is not available on the website. Usually items will be listed even when out of stock, but not the case with this one.May no longer be available.
Just had a look at the Toolstation site but no mention of broaching oil at £4.29 a litre. There is pipe threading oil at £6.63 a litre and tapping and drilling spray at about £3.50 a can. I have used the spray before on aluminium and it worked fine but a spray can does not last long. I may give the pipe threading oil a go for general machining and see if it is worhtwhile.The free carriage is a real plus with Toolstation, they can't make any money on small heavy orders.
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