Member postings for Martin Connelly

If the threaded bushes are brass you could consider making a long tap with a long pilot on the end to cut the threads in both bushes. As long as it is sharp steel it probably will not need hardening for a one-off job. You can then single point cut the tube threads on a lathe to ensure they are pitched correctly. You can do the same pitch and different diameters if that is what is needed.

Martin C

I don't think the thread form needs to be so perfect that a modified angle would be required. I cut the threads until the collet threads on to the part loosely enough to ensure the self screwing action under load. It is important to polish the thread enough to reduce friction as well (a number of passes with Scotchbrite for example). This means that if the angle is slightly wrong you would just be cutting the thread slightly deeper to compensate. The important features are the diameter is correct and the centre drilling in the end is on centre. Mouse could do as I have done for a lot of tooling, modify (or get someone else to supply) an ER parallel shank collet holder to suit a 16mm collet if he wants to make use of this collet holder and collets beyond just buying threaded tooling. I have also centre drilled and cut the required thread onto, amongst other things, the shanks of a Ø16 insert milling cutter, a fly cutter and a set of "Little Hoggers".

Martin C

It occurs to me that threading carbide is probably not going to be as hard as drilling the centre in the end of it. There is also the risk of brittle threads in carbide shearing off. I would put carbide tooling in my modified ER holder or use my standard ER collet holder in the spindle.

Edited By Martin Connelly on 23/06/2023 08:39:55

The collets have a threaded bore to suit threaded shank tooling. They will not close down on a plain shank tool. You need something like this. The centre drilling fits over the point in the back of the collet holder.

Martin C

Petrol is a blend of different compounds and there will always be something that will evaporate faster than whatever is left from the original blend. This is why old petrol is dodgy whatever the quantity of ethanol it starts off with.

Martin C

Cross slide.

I often use a morse taper extension in the tailstock for this reason. MT2 to MT2 for my lathe. It's often said you need to spend more on tooling than on the machine. The current discussion on QCTP Vs. 4 way tool post, for example, mentions cost being significant. This extension may be one more thing you will need at some point.

Martin C

DC31k, like this? Tapped and plugged the end with a suitable bolt then cut off the excess, faced and drilled the centre before adding the thread.

Martin C

We had a manually operated Hilmor draw bending machine for very thin wall, small bore tubes in stainless steel. An example can be seen here (but may disappear at some point in the future as it is an auction site) Hilmor tube bending machine

Most people are likely to have heard of Hilmor as they make tube benders used for copper pipe in domestic and industrial settings.

Mandrel draw benders like this support the tube being bent with an internal mandrel that stays at the point where bending takes place as the tube is drawn past the mandrel and the bend progresses along the length of the tube. It can take some force to withdraw the mandrel after bending which is why there is a big lever at one end of the bed to do it. They rely on a bend die made to the required tube size and the required bend radius with a close fitting mandrel. They also have a follower die that matches the tube outside diameter. This means the tube is supported all around the circumference by the bend die and the follower and internally by the mandrel. I don't suggest anyone here wants to go as far as making a tube bender with a mandrel. If you are going to make a bending tool I would suggest that you have a bend die and follower that suits the outside diameter of the tube you want to build.

If you look at the copper pipe bending tools for Ø15mm and Ø22mm you will see that the bend die has a U shaped groove and that the follower fits into this groove to keep it correctly aligned. The follower is then used to push the tube around the bend by a roller on a lever. In order to avoid crushing the tube the pressure on the follower is usually some distance ahead of the point where the bend is taking place. Benders for copper pipes have this set as the material is a known factor. To get this correct the roller position on home made tooling means this may need to be adjustable. The Hilmor press benders we used at work had a leadscrew that was operated by turning the handle on the end of the lever (adjustable bending lever) , this also allowed the use of different bend dies for different radii and diameters. Set the roller too tight and you crushed the tube on the inside of the bend, too loose and the bend radius and ovality started to increase.

Paul said in 2022 that bending was one of the least accurate industrial processes. We used to bend anything from 1/4" tube up to 2" NB on one CNC bending machine to tolerances of ±0.1mm on lengths and ±0.1° on angles. Try and get something welded to that tolerance.

Martin C

Edited By Martin Connelly on 12/06/2023 13:03:37

I expect the "temporary" description is due to the fact that the thread dial is redundant on an inch based leadscrew being used to cut metric threads. It would be expected that you would not want to leave it in that state if you were cutting a lot of threads. However for a non-industry user the extra time taken of having to leave the half nuts engaged and reversing the drive is not going to have a cost. Additionally, if you cannot reverse the motor on the lathe then you will need to hand wind the spindle backwards for each pass. Doing a lot of metric threads would soon become tiresome. There is also the slight risk of a screw on chuck unwinding, not a problem if using in the spindle collets.

Martin C

Duncan, I was replying based on Justin's question of what to do if he only had something to make a Ø36 hole. That to me implies he has something that will cut that specific size. The options for that are, in my mind, hole saw, annular cutter or drill, maybe a step drill. I was not suggesting going out and spending money on a special tool for this job. Having a selection of hole saws and annular cutters myself they are what I would use to make a large hole to start with in a 3mm thick plate. And I do have a Ø36 annular cutter if you are wondering.

Martin C

Hole saw or Rotabroach type annular cutter in a tailstock is a good start to save time drilling and boring. I think this is what you are thinking. A large drill that size in a lathe and in material that is that thin may cause problems.

Martin C

The coiled phone cables that always ended up as a tangle were made tight by moulding them loose then reversing the direction of the coil similar to the post heat treatment move in the video. It may also be used on the coiled nylon air lines that also end up as a tangle.

Martin C

One of these, photo taken 2014.

Martin C

I don't know what you have in the way of other equipment but the cheapest solution would be to grind a pointed tool to make the grooves and put it in a basic fly cutter. You are only cutting brass so the tool does not need to be anything particularly hard. You can move the ground tool in the fly cutter to do different diameters of concentric grooves. Piece of hacksaw blade may be enough.

Martin C

Edited By Martin Connelly on 01/06/2023 10:37:11

I found some in A2 stainless from Spalding Fasteners that are 1/2" long. It's easy to shorten a slightly long screw.

Martin C

As David says "The dial indicator MUST be on center height." He means the contact point of the indicator's arm but you probably understand that but so must the point of the tool cutting the taper. They need to at a matched height even if slightly higher or lower than ideal.

Martin C

They don't look hard to make but a drawing showing material, dimensions and thread would be required to progress to manufacturing.

The other alternative is to pass the nut to someone who can use it as a prototype and copy it.

A rough guide to where you are would help with the second option.

Martin C

We had M14x1 on something at work, can't exactly remember what but I think it was part of a hydraulic hub fitting kit and possibly Italian.

Martin C

What is often the most important thing is to make sure the tool is cutting and not rubbing and not overheating. If you are producing filings or smaller then you are probably not cutting the material away, more likely rubbing it away. This drastically reduces the life of the tool. There are also maximum speeds for the cutting edge. Going faster with, for example, high speed steel, than the recommended maximum for the cutter and material combination will probably cause overheating and reduce the tool life. Flood coolant is going to help if you are close to maximum but usually it is better to be below the maximum. These speeds can be found with a simple Google search for speeds and feeds calculators to find the maximum RPM then pick something about 50%-75% of it. The feed rates are a moot point if you are hand feeding so go for discrete chips not dust of fine filings. Note that a 4 flute cutter needs to be fed at twice the rate of a 2 flute cutter to get the same chips. With experience of your machine and what you are doing you will learn if you can go faster or slower as the work requires.

The problem with the listening to the sound method is that with some jobs there may be a lot of re-cutting of chips in the work area and this will make a lot more noise than a job where the chips are flung away from the tool.

Martin C

Your are suffering from basic mechanical problems. First off the small pitch of a threaded rod requires a high RPM to achieve rapid motion along it. This high RPM has to overcome the resistance due friction from a less than ideal material match between the basic threaded rod and the nut that is running on it. A typical machine tool would have a pitch something like 2.5mm, 3mm, 4mm. These allow rapid motion with lower RPM. They also have a better material than stainless steel and the mild steel threaded block. Typically machines have well made, polished, stiff leadscrews and brass or bronze nuts for low resistance. CNC machines tend to use ball nuts and matching ball screws to reduce the friction as much as possible to achieve the high transit speeds you are trying for. Secondly the U channel is also stainless. Stainless steel is not usually used for sliding surfaces because there are usually better options.

A typical router does not rely on metal to metal sliding surfaces, they may use bearings as wheels to give low resistance to movement. Mills and lathes have lubricated flat contact surfaces that are carefully made for low friction. This complexity is justified as it is a one off cost that fixes friction problems. Remember that once you actually start using what you are designing there will be additional forces acting on the sliding parts and these will increase the friction of all sliding surfaces. By not reducing all this friction you may get something that will move when not doing any work but stalls the moment you try to use it on a workpiece. Ian P mentioned whip in a long slender rod spinning at 1000rpm. Even a small amount of whip will increase the friction inducing forces. This is why at low rpm the effort needed to turn the rod and move the carriage is low but at high RPM it stalls.

Martin C

Edited By Martin Connelly on 20/05/2023 07:44:06