Member postings for Andrew Johnston

A basic surface grinder is all that is needed. The required angles and placement of the dies is taken care of by fixtures:

Andrew

If the Whitworth dies are for free I'd definitely acquire them. Assuming they are in sets they have a value in the Uk.

Andrew

This picture should give you some guidance as to the size of the dies for a given size of head:

There are four dies per set, labelled 1 to 4. Not only do the thread type and die type have to match for all dies in a set there is also an arbitrary number on the dies which needs to be same for all dies in a set. The arbitrary number is related to the numbers on a tapered rule used when sharpening the dies, 51 in this case:

Andrew

The designator listed is a description of the type and hand of the boring bar, not the inserts it takes. I would expect the boring bar to take CC**09 inserts.

Andrew

Who cares!

I use metric and imperial, both for hobby and commercial machining as appropriate. But then again I'm making parts, not sitting in my armchair.

Andrew

The spigot on my Clarkson Dedlock holder is definitely 1" OD, 12tpi Whitworth thread form, and is 2-start.

Plenty of Dedlock holders on Ebay, which is a sure sign they are obsolete. I have enough Dedlock cutters to make it worthwhile having a holder. Like this one:

Andrew

Is the pattern a helix or a series of concentric circles? What type of lathe and tooling?

Andrew

Having used both to make nuts, bolts and studs, personally I think that a repetition lathe is better suited than a capstan unit. Although, as always, it comes down to tooling. I have a Britan which has a small footprint, similar to a Myford. I normally use a Coventry diehead for external threads. But a clever holder with dog clutches allows an ordinary split die to be used almost as quickly as a diehead:

Andrew

My experience of those type of sets is that after unpacking you should put them directly in the bin. Then go and buy quality taps and dies.

Andrew

Depends what you want to do with it. I have a capstan unit for my lathe (Harrison M300) which has its uses, but it is not as useful as a proper capstan lathe. Also note that a capstan unit, or lathe, is useless without tooling. For quantity production I have a repetition lathe; far quicker and more versatile for small items than the capstan unit plus centre lathe.

Andrew

Have you ever made anything yourself?

Andrew

Oh dear, I come out as almost 100% engineer.

Andrew

On aircraft, high tensile bolts (designated by notches on the periphery of the hexagon head) were often used with standard nuts.

Andrew

Short answer is yes. The main spindle on my CNC mill goes from 100 to 5100rpm in two overlapping ranges. For small cutters I have added a high speed spindle that goes to 24000rpm .

Andrew

Castellated swarf:

And formed swarf from an insert parting off tool:

Andrew

Folded heatsinks are very soft and gummy, probably near pure aluminium Extruded heatsinks are aluminium alloy, albeit not the nicest material to machine.

I've machined and tapped a lot of heatsinks for work. I tend to drill for about 50% thread engagement. An M2.5 by 8mm hole is doable with ordinary uncoated hand taps. But it's not great design, so I'd change the design to shorten the thread depth. I usually tap dry as I don't want to contaminate the heatsink and electronics.

Andrew

The width of the tooth at the pitch circle diameter is not dependent upon pressure angle. But larger pressure angles gives a tooth that is more triangular in shape.

Andrew

If we assume that the OD and depth of cut are correct then the next question is: are all the teeth the same width, but too narrow, or does the tooth width vary around the periphery?

Out of idle curiosity which number involute cutter did you use?

Andrew

The OD is correct. Total depth is correct for the standard depth of 2.157/DP. But tooth depth can vary; typically 2.25/DP for low tooth counts and 2.125/DP for large tooth counts. The total depth should be marked on the cutter, often as D+f.

A face on picture would be helpful.

Andrew

At the midpoint of the tooth the width of the tooth, and of the space, should be the same. If the teeth look thinner then something is wrong. What diameter was the OD of the blank?

If you want to cut "proper" bevel gears, which are designed using the DP at the outer face, then you will need special 'bevel' involute cutters. As far as I know these are obsolete and unobtainable. If you cut bevel gears using the parallel depth method, where the design is done using the DP at the inner face, then normal imvolute cutters are fine.

Andrew