Member postings for Andrew Johnston

I am flummoxed by the idea of creating a part in an assembly, ie, the shaft in an assembly of gears. How does one then create a 2D drawing of the shaft that doesn't exist as a seperate part?

I prefer to create seperate parts, that represent the parts I wlll actually make. When creating a part I don't sweat over dimensions initially. Just create all the features I need to create a part that is topologically correct. I can then go back and add dimensions.

Assemblies are created from individual parts, using constrains as needed. Just as one would build the physical item. I only use constraints that are strictly necessary. Not only is an assembly used to make sure holes in mating parts line up for instance, it is also used to make sure that parts fit together and move correctly when the assembled parts move, as they would in reality. Like this assembly of the motion work on my traction engines:

I tend to design gears complete with accurate tooth forms. Here is a bevel gear model:

An assembly to check meshing:

And reality after CNC machining:

The bevel gear PCD is 1" at the outer end.

Andrew

Decent quality slitting saws, on a good arbor, should run with negligible side to side wobble. Radial runout is another matter. Even on industrial machines, and arbors, they run out enough to hear the change in note as the saw rotates.

Andrew

Really?

Andrew

Just because it looks like a grease nipple doesn't mean it is for grease - RTM.

Andrew

Just because it is marked Vertex doesn't mean it was made by them. It would be helpful to know where you are based and who you are buying from.

Andrew

Use a ruler! Looks like there are about 6 thread pitches on the screw. Measure across the six pitches, metric and imperial. Dividing one my t'other, and inverting for imperial, will give an estimate of pitch (metric) or tpi (imperial) to 5% or so. Could be metric, imperial British or imperial US.

Looking at the height of the screw the pitch appears to be about 1mm aka ~25tpi. The diameter doesn't seem to agree with any particular thread standard, other than 7/32" BSW, which wouid be an unusual choice.

Andrew

None of my boring bars (home made or commercial) have flats. Same as Jason, none have ever been marked. The grub screws should be flat and smooth on the bearing end. The only exception are the horizontal extension bars on my commercial boring heads, which have flats. That is because they are subject to higher torque than a boring bar. If anyone doesn't know what I mean by extension bars I can post a picture.

Andrew

The salesman is a clueless idiot.

A stickout of 120mm is far too much. A rule of thumb is 5 times the boring bar diameter, so 60mm in this case. My experience of using inserts, even with a high end industrial boring head, is that they are very prone to chatter. So much so that I have reverted to HSS toolbits; as in this setup:

The home made boring bar is 7/8" diameter and stickout is about 6", so more than the rule of five times. I initially used an insert boring bar, but it chattered badly, so I quickly reverted to HSS.

My 50mm Soba boring head came with several HSS boring bars, all about 75mm overall, so around 40mm stickout. After grinding they sort of worked but at least they didn't chatter.

Andrew

It's a stock code, not an ISO insert type. Which is why i said the insert type wasn't mentioned. Fine if one wants to order from Chester, useless if one wants to order from elsewhere.

Andrew

The insert type doesn't seem to be mentioned on the appropriate Chester product page. That's a red flag and means I'd avoid the cutter like the plague. The inserts are probably not standard and/or not common. So you have to buy them from Chester.

Andrew

On my A&S made Bridgeport it says on the connector they are made by LPA. Rather to my surprise LPA are still going and are relatively close to me, in Saffron Walden.

LPA Group

The part number on my connector is X4S which is part of the LPA Niphan industrial connector range. However the push fit/panel mount version appears to be obsolete. The group as a whole seem to be heavy industrial so their products are unlikely to be stocked by distributors.

Andrew

Following on from Nigel's post my 4-way toolpost is sort of indexing, every 9 degrees. In the above picture of the copy unit the indexing plate can just be seen lower left. That is one reason I never fitted the Dickson toolpost.

I keep meaning to machine a single block shim to the correct thickness for my commonly used tools, but have never quite been irritated enough when changing tools to do so.

Andrew

I agree with the previous posters; I don't bother with a QCTP for the same reasons. Early on I bought a Dickson toolpost and some holders, but never fitted it, and never will.

Most of my turning is done with four tools; a RH knife tool, RH oblique tool to use the other corner on the inserts, parting off blade and a boring bar. If I need to change tools on a job it is simple to keep the shims with the tool after initial setup. Centre height isn't as critical as is made out; I line up by eye against a centre in the tailstock.

I can't comment on ball turning units as I've never used one. For handles and non-critical work I chamfer and then use files. For more precise work I use a hydraulic copy unit:

It came with a custom Dickson toolpost, so I use it. That's my excuse and I am sticking to it.

Andrew

Oh dear, as usual I am out of step, on the vertical mill I use the quill:

I sometimes use the quill lever for roughing, but mostly use the power downfeed on the quill as I am lazy, and it gives a more consistent finish.

For deep holes, that exceed the quill travel, I use the horizontal mill:

Andrew

Nothing to do with that; it's all down to cost of manufacture. Once a mold is produced it costs pence to churn out plastic gears.

Andrew

The arrangement is not a bodge. Any of the four combinations of BSP parallel and taper is acceptable, provided one understands the limitations.

BSPP = parallel thread

BSPT = tapered thread

BSPP external to BSPP internal - not regarded as pressure tight, ie, the seal is made by the threads themselves. Mainly used for non-pressure glands and fittings, or where pressure tightness is achieved by other means such as tapered cones on the pipe and recesses

BSPP external to BSPT internal - not regarded as creating a pressure tight joint using the thread alone, not much used

BSPT external to BSPP internal - can provide a pressure tight joint using the thread alone. It is relatively easy to create a tapered external thead compared to a tapered internal thread, so this combination is a good compromise. Of course some additional sealing can provide belt and braces.

BSPT external to BSPT internal - provides a pressure tight joint using the thread alone

Andrew

Wrong!

Take a VFD and an induction motor designed to run at 50Hz. At 50Hz the associated speed is called base speed, and rated power will be obtained with the rated voltage applied.

Above 50Hz the rated voltage is not enough to maintain costant phase currents, so the torque falls off. But the speed increases, and since power is torque time speed the power stays constant. Which is what I think SoD meant to say.

Andrew

Look at the finish, pretty rough for machined surfaces.

Andrew

Much more likely to have been cast and then cleaned up, probably by hand.

Andrew

That was my initlal thought but it does tie in the with datasheet.

I think the OP is under a misapprehension, medium carbon steels are not intended for hardening and tempering in the same way as silver steel or gauge plate. Instead the heat treatment is more about optimising impact resistance and yield point. For medium carbon and alloy steels tempering at temperatures normally used for silver steel can reduce the impact resistance.

Before deciding upon a material what are the important qualities? For instance surface hardness, ductility or impact resistance?

Andrew