PDA

View Full Version : Need some mods on a tool rest banjo



bilbo
12th March 2018, 05:35 PM
G'day all,

I have a Sherwood lathe that I purchased in "as new condition” but I keep getting told “it’s one of the old models”. As a result, nothing fits and everything in today’s spare parts doesn’t fit. My new concern is the tool rest banjo that sits across the lathe bed and takes the stem of the tool rest in it. The stem is 22mm or 7/8 ths which seems to be an uncommon size these days. Either 25mm (one inch) or 15mm is more the go. I have two identical banjos of 22m that I want to get bored out to take a 25mm tool rest, so I can make use of a greater selection of tool rests such as the curved bowl rests. Does anyone know an engineering shop around Perth that can bore out or drill out from 22mm to 25mm?
I reckon the wall thickness after drilling to 25mm will still be enough to take the torque as these Sherwoods are way overbuilt; there’s nothing dainty about them.

My efforts to actually buy a 25mm banjo have resulted in several wasted, hair tearing journeys to suppliers that want to sell me anything but that! I even had one the other day that was something really odd - 20mm?? Good job I checked it before I left for home!

Thanks.

Paul39
20th March 2018, 11:26 AM
Bilbo,

You might try over here to see if someone can refer you or do the work: Metal Work Forums (http://metalworkforums.com/)

I looked for an engineering shop in Perth, what came up were big shops touting CNC machines. You need a shop that repairs construction and agriculture machines.

Failing to find someone who will bore out the banjos for less than a new lathe, you could wrap some 80 grit around a 20 mm dowel and get to grinding.

If you have a stout drill press or have a mate with one, buy a 1/2 inch shank 25mm / 1 inch drill, center the bit over the banjo hole, securely clamp down the banjo and have a go. Slow drilling speed and lots of downforce.

chambezio
20th March 2018, 12:32 PM
Send a message to BobL. He may be able to oblige. Failing that he may be able to point you in the right direction. It is a simple task and does not require high precision.

BobL
20th March 2018, 05:43 PM
Shoot me a PM bilbo.

I have all the gear needed for a reasonably precise fit.
Chances are that just drilling a hole in the banjo with a 25mm bit will generate a sloppy hole that is slightly more than 25 mm in diameter.
A test drill in some cast iron will tell us the true size of the hole it drills.
If the hole is too sloppy then the best way to do it is to drill a 24.5 mm hole and then ream the hole out till it fits the tool post.
It so happens I am in the process of making a second banjo from scratch for my Woodfast so I am "in the zone" so to speak!

skot
20th March 2018, 07:13 PM
Stainless steel rod comes in 22mm.

Have you considered purchasing a length of SS 22mm rod from a steel merchant....approx 0.5 m long and taking it to a welding shop/factory. They could cut a 200mm length for the stem and the remaining 300mm would form the cross bar.

Those places can weld SS.

I did this when I was too impatient to wait for a small rest to arrive from Vicmarc and the local welding works whipped one up for me for my pen turning. Cost my $20 and he provided the SS which was an offcut from an old job.

bueller
20th March 2018, 07:28 PM
Yeah I’d be looking at having the tool rests made over modifying the banjo, I had Vicmarc make me some in 7/8 size when I couldn’t find any online.

BobL
20th March 2018, 08:16 PM
Stainless steel rod comes in 22mm.

Have you considered purchasing a length of SS 22mm rod from a steel merchant....approx 0.5 m long and taking it to a welding shop/factory. They could cut a 200mm length for the stem and the remaining 300mm would form the cross bar. .

I've made some T-bar type tool posts for my Woodfast and have to say they are not my first preference.
Instead the tool posts I like using have cross sections that look like this.

432057
This profile enables chisel support close to the work, and for the fingers holding the front end of the chisel to tuck neatly under and slide along the tool post and remain protected.
This one was made by welding square stock to flat bar and then grinding the radius

Given the OP already has a stock of 25mm tool posts it would seem smarter to bore the banjo than to modify every tool post or make a new range of tool posts.
If the OP requires I can turn up a 25-22 mm sleeve that can be popped into the banjo to convert it back to 22mm at any time.
This will be much less work than making a whole bunch of new tool posts.

bilbo
25th March 2018, 09:10 PM
I reckon I'll go with the BobL idea and I have a 25 mm drill arriving soon. Drill out to 25mm and then make a cupppla sleeves that will reduce that if I ever want to go back to the smaller 5/8ths or 7/8ths.

KBs PensNmore
25th March 2018, 10:28 PM
Before you start, make sure that your drill press can drop its revs to around 400 or lower, anything much higher than that and you'll have a strange looking hole. You'll need a real sturdy drill press to do this, I've a 16 speed DP and 25mm scares the beejeezus out of me.
Kryn

BobL
25th March 2018, 11:09 PM
400 rpm is a typical recommendation for a 25mm drill in cast iron

However, remember this setup is not solid cast iron, Its only drilling out a 1.5mm cylinder of cast iron from the sides of an existing 22 mm hole
Running the bit at 400 rpm may result in the bit grabbing the work and jamming in the hole or worse, split the whole thing open.

Unless the work piece is really well held it's unlikely that it will drill close to a 25 mmm hole but something larger.
This why would drill a 24.5 mm hole (it might come out to be 24.7mm) and then ream out the remainder.

Either way I would be running the bit much slower than 400 rpm, maybe 200 rpm.
It might also be worth considering plugging the hole with a plug of hardwood to make sure the drill does not grab.
Maybe drill a 5 mm pilot hole?

On the plus side most cast iron has so much carbon in it this makes it self lubricating.

ronboult
28th March 2018, 05:04 PM
Hi bilbo
You will get a much better fit if you find someone with a mill and boring head. The hole can then be bored to an exact slip fit
Good luck
Ron

bilbo
31st March 2018, 01:40 PM
I really tried to simply purchase a 25 mm banjo here in Perth. I've now given up on that and gone back to the 25mm drilling idea. I bought the reduced shank drill for about 30 bucks and drilled one of the two 7/8ths banjos that I have. Because the drill was binding due to the depth, the drill lands were staring to wear badly. So I switched to drilling from the other end. The two holes met reasonably well and came out dead-on 25 mm each, checked with a vernier. There's a slight misalignment of the holes of about "I can feel it with my fingernail" thickness but all said n done, it's come out of it quite well. A bit of filing ad I reckon it'll work. It will certainly be a tight fit and if I was doing this again, I'd go 26mm rather than 25mm. However, 26 mm drill may leave the banjo wall thickness a bit thin. I need to get a normal 25mm banjo to see it in action. More soon.

ronboult
31st March 2018, 02:56 PM
Bilbo
if the 25mm drill hole is a bit tight then a 1inch drill (25.4mm)will give a bit of clearance. Alternatively a layer of emery wrapped around a piece of dowel with a slit in it to hold the emery will allow you to remove the step and sneak up on the size required. I suggest you dont want to make it too sloppy.
Ron

Bohdan
31st March 2018, 03:01 PM
An alternative solution is to use a brake cylinder honing kit (the kind with the three abrasive stones) to open the hole and smooth it out.

BobL
31st March 2018, 03:27 PM
If you want to borrow an adjustable reamer from me feel free to ask.

bilbo
31st March 2018, 06:38 PM
Bob, I use to be heavy machinery and truck mechanic in my younger day but when I got out of the trade (for good!) I sold a full set of adjustable reamers! They were in beautiful wooden case and went from something like 3/8ths up to well over an inch. This is the first time in 45 years that I've regretted it.Oh well, that's life! I'll have a go with the dowel and paper but knowing the tolerances (or lack thereof) on Chinese made metal parts I'll prolly get away with it! Thanks guy,more soon when I buy my new set of "one inch" tool rests.

BobL
31st March 2018, 06:48 PM
Bob, I use to be heavy machinery and truck mechanic in my younger day but when I got out of the trade (for good!) I sold a full set of adjustable reamers! They were in beautiful wooden case and went from something like 3/8ths up to well over an inch. This is the first time in 45 years that I've regretted it.Oh well, that's life! I'll have a go with the dowel and paper but knowing the tolerances (or lack thereof) on Chinese made metal parts I'll prolly get away with it! Thanks guy,more soon when I buy my new set of "one inch" tool rests.

No worries.
If you want to speed up the sanding process use a half in steel rod with a slot cut in it for a strip of wet and dry paper (wound the right way) and put the rod in a drill press, if will be a lot faster than doing it by hand. don't run the DP too fast and you should be OK.