Interfering with fits?

You were clear enough, it's that the reamer may leave a hole in the plug larger than ideal. With a 24mm hole in the plug you will be well advised to drill out to say 20mm and then bore to reaming size , this ensures the reamer follows a true path rather than the path of the drill which can wander.

So may as well go the whole hog and bore the last little bit to finished exact size and save the cost of the reamer for something else.

One other spanner to throw into the works is that the wheels on my belt sanders can get too hot to touch after prolonged use which could affect the fit if shrinking.

One other spanner to throw into the works is that the wheels on my belt sanders can get too hot to touch after prolonged use which could affect the fit if shrinking.

I’m not sure that that is appliccable if the coefficients of expansion are identical, or nearly so. Both wheel and bush would be at the same temperature at the interface?

Okay right so I'll bore everything and forget about the reamer.

Yes, I suppose they should expand and contract together so that should be alright. I've never noticed the back wheel getting massively hot, but I don't tend to touch it much!

The only issue I can think of will be the difficulty of heating the wheel and cooling the plug at the same time, since I don't have a freezer in the workshop. I'll have to heat up the wheel, pop in the house and grab the plug from the freezer, then heat the wheel back up again, then press it in.

Another issue will be recutting the keyway! I'll worry about that later...

I'll have a go at this soon and update you all. Thank you all for your comments so far!

The domestic oven is a fine device for gently and controllably heating a part for shrink fitting purposes, and is usually conveniently located near the freezer Just remember to clean any oil off first.

Nice belt sander, is it Jeremy Schmidt's design?

Ah yeah that's a good idea too. It's made me think, I have a small electric oven in the workshop which I usually use to temper metal. That should get hot enough and have enough space for the wheel.

Thank you, no it's not Jeremy Schmidt's design, its my own design of an amalgamation of my favorite features of ones I've seen. Plus a few different choices to make it easier for me to make with the tools I have available. I have the Solidworks design if anyone wants it, but it's relatively specific to the motor I had already, and uses the metal sizes my local metal place has.

and most inportantly wait till SHMBO has gone out

"and most importantly wait till SWTSMBO has gone out"

WHY?

Bits tempered or "Blued" in domestic oven, usually on a Sunday AFTER roast done when oven is already hot (Yorkshire cost saving trait). Do you put greasy parts In? Can't think of ANY oven usage that would cause "Contamination" My bits are ALWAYS clean before loading. Do you wait before using the big cooling box?

Regards Ian.

Not Aluminium into steel, but when I wanted to shrink fit a steel shaftv into a cast iron base, I chose 0.001" (0.0254 mm ) interference.

cast Iron base was reamed to 1", and measured.

Steel shaft was turned own to measured diameter+0.001"

The shaft spent the night in the freezer, and the 6" diameter x 1.25" thick cast iron was cleaned and with permission heated in the oven at gas mark 6.

The shaft was removed from the freezer and wrapped in a towel, while thge base was moved from the oven onto a piece of 10 mm ply on the kitchen floor.

Shaft unwrapped and was a nice fit into the base. The frost on the shaft gradually disappered upwards.

When cool; a tight fit.

Based on industrial experience, Loctite usually needs a clearance of 0..002 - 0.003", You are relying on the shear strength of the anaerobic. So choose the correct grade, such as a retaining compound, not one intended to provide a relatively easy disassembly in the future.

Howard

Edited By Howard Lewis on 17/08/2021 16:45:45

Progress update, today I managed to turn the plug to size. It ended up at around 39.985mm.

So I bored the hole out to 39.905mm, somehow it worked out perfectly.

Then straight off into the oven, and the plug into the freezer. Left them both an hour. Then it slipped right in. Pretty much immediately wouldn't come back out. I left it to cool, then chucked it back up and faced each side. Then on the second face I drilled and bored to 24mm

It's nice how the plug sort of disappeared when I faced it

Thanks to everyone for their help so far.

However, I could do with some advice on the next task.

I now need to cut a keyway in the bore to accept an 8mm key, about 3mm deep. Last time the wheel was made, I managed to cut the keyway in myself using a piece of 8mm hss which I ground a bit of relief on, then i just took passes to shave off bits. This worked with varying success and I ended up having to file the slot a bit more to get it to fit.

Does anyone have any tips on what sort of angles I should try to grind into the cutting tool or any tips in general for cutting a keyway in a lathe.

Looking good Richard!!

Phil

Nicely done, Richard

… and you’ve saved the price of a bottle of 638

MichaelG.

Well done. Axles have wheels shrink fitted for railway stock and likely tires are shrink fitted to recondition worn wheels, too. Nearly every starter ring on car flywheels are shrink fitted.

Belt and braces for fitting different gear parts together leads me to first fit the parts together (the belt part) and add a couple of threaded holes across the join, then loctite in some threaded rod, bolt or grub screw (the braces). Machine flat if necessary. This lot has left me with a very safe modification, even if tolerances are not quite perfect…

If I were to fit the ‘braces part’ in this instance, because the wheel is possibly rotating at 2800rpm, I would be careful to drill the holes to identical depth and insert identical grub screws. They would be close to the axis, but this would minimise any likelihood of altering the balance.

When I did the two 4mm keyways in the steel rollers below, I used gauge plate (Ground Flat Stock) simply because it can be milled & filed to an accurate slot 'cutter' shape before hardening with far greater control of the shape (esp. the corners) than can be achieved with HSS offhand on a bench grinder.. ..made for a crisper slot that didn't need any dressing..

The 'rake' on the front cutting edge was deliberately left steep to prevent 'digging in'..

I gave relief to all sides, only the cutting edge and a short distance above it was at finished dimension, final few licks with a stone after hardening.. ..looks a bit rough, but only the cutting edge on the front corner has to be 'good'..

I think 8mm is a bit wider than I would like to plane on the lathe all in one width, could probably do it with a tool like you used before say 3mm wide. Set it above ctr height and do one narrow keyway, then same distance below ctr to form as second and then take out the bit between with the tool on ctr height. Doing it in that order is more likely to give a parallel keyway as if you did the middle first the other two cuts would try to wander into the gap.

If you use a tool holder like a boring bar and a 3mm dia HSS bit ground like a parting tool but on it's side that will work. Similar to this just a square profile to the cutter.

Agree that Jason's method seems far more likely to result in success

Hi Richard,

I would not recommend pressing aluminium into aluminium. There is too high a tendency for the aluminium insert to pick-up as it is being pressed in. When I have to fit aluminium to aluminium it is usually a light press fit, no more than +0.01 mm with a smear of Loctite to stop the "picking up".

Preference would be to go for a mild steel insert. If you are adamant you want to do a press fit then for 38 mm diameter you need to have your insert larger than the H7 bore, (0.0 to +0.25 mm) by +0.034 to +0.050 mm for an r6, or interference fit.

You will probably need a good arbor press to get these parts together.

If it were me, I would go with Tony, 0.01 mm down on diameter and Loctite 638 and possibly with one band of straight knurl on the last part of the insert to go into the hole. The band of knurl will also need some effort to get the insert into the hole, so be prepared if you do this. The important part is to leave the assembly to cure for 24 hours.

Regards

Gray,

Ignore my post things have moved on since I started typing.

Edited By Graham Meek on 20/08/2021 11:19:48

To make life easierv on machine, tool ,a nd you.

Make a sacrificial plug to go into the bore, and then drill a hole, centred on the boundary between sacrificial plug and bore.. This will remove a lot of the material that needs not to be there.

Remove plug and cut keyway.

You can either hold the tool in the tailstiock in some way, or in the toolpost, (Obviously equally disposed vertically about the centreline ) and then rack the tool to and fro, using the Saddle or tailstock handwheel..

The toolpost method is better since the Cross Slide can be used to control the depth of cut.

Once, I did cut a square hole, using a tool in the tailstock, but bit was laborious, since I had virtually no control over depth of cut. The method was to cut as deep as possible, about 0.010", withdraw, rotate chuck by 90 degrees, and repeat. Continue repeating until hole was to completed depth. Crude, and slow, but it produced the desired result. Not that I would want to make a habit of it!

With 20/20 hindsight, should have mounted the tool in the Toolpost!being bone idle, the tool was ground on the front face only, so that the swarf had to be cleared on each backstroke. Should have been ground like a small parting tool, with clearance on both sides.

Howard

Thanks everyone, I'm really happy with the results so far.

Not done it yet- That sounds like a good idea, just to go the extra mile and add a bit more. I'll put some m5 set screws along the joint

Howard- I've ran out of aluminium so I won't be able to make a plug and drill the bulk out. But that does sound like a good idea for the future. I really should have worked it out and drilled the hole before I bored the center out.

I've been away in Ireland this weekend, so I'll attempt to cut the keyway tomorrow afternoon.

I think I have a boring bar type tool that would be perfect. The only issue I can think of so far is that I can't use by belt sander to shape any cutters so I'll have to get the bench grinder reassembled.

What sort of depth of cut should I look at trying to take?

I'll try to make a tool smaller than 8mm, perhaps 4mm then I can do it in two passes. If diogenesII did 4mm in steel then I imagine 4mm in aluminium will be fine

The sacrificial plug does not have to be Aluminium. It would be better if it was, to lessen the risk of the drill wandering.

The object of drilling is to remove as much metal from what is going to be the keyway, leaving less for the keyway cutting tool to remove.

FWIW, having drilled the hole, when you start to cut the keyway, don't be greedy, better to succeed after lots of 0.005" cuts rather than trying a few 0.050" cuts and failing and possibly damaging tool, set up and workpiece.

A tool 4 mm wide / deep won't be strong, so small cuts have to the order of the day.

Once, I produced a 1/8" square, blind, hole in brass, by drilling a 1/8" hole and then forcing a 1/8" toolbit in for 0.010", withdraw, rotate chuck 90 degrees repeat, and then repeating and repeating until I had the square hole of the depth that was required.

Slow? Yes, but it produced what was required (An extension for a speedometer cable )

I would be thinking in terms of the workpiece in the chuck, and a 4 mm toolbit, mounted in the toolpost, equally about the lathe centreline, with the cut ( 0.050 mm? ) being gradually applied by moving the Cross Slide and racking the Saddle too and fro.

I made a Peter Robinson Slotting Tool, and adapted it to my larger lathe , and have used that to cut keyways quite successfully. But am unsure if College Engineering Supplies still sell the casting.

Howard

I think Jason's suggestion of making a 3mm wide tool, cutting two separate slots, and then clearing the central 'upstand' is a good one, and more likely to give you a straight-sided slot at the end of the job.. ..if you try to do two 4mm 'bites', the first will be okay, but the tool will want to wander into the 'open' side on the second pass..

The depths of each cut should be shallow - try 0.02mm / .001" and see how it goes, I found the job went quicker taking shallow cuts and just turning the cross-slide round a division or so with one hand whilst racking the saddle with the other - a human approximation to a shaping machine..

In any case you will be able to feel whether you can take a bit more or need to take a bit less, once you get started.

You might be able to grind the necessary reliefs around the end of a small piece of HSS off-hand on a benchgrinder - only the cutting edge itself really has to be straight (-ish), as long as the rest of the tool 'body' has a little clearance so that it doesn't rub on the sides or base, it doesn't have to be particularly accurate or even in this manual operation - a Dremel might do it..

Taking some care to make sure the cutting corner is 'sharp' pays dividends, it becomes tiresomely hard work with a dull cutter.