reamer size, what do I need.

[Speedy]

what size reamer would I need so the diameter of a bolt can slide in but tight.
using both M2 and M2.5 hardware. so one reamer for each.

and on that note are all M2 and M2.5 taps the same? seems like I can get a few taps from hongkong on ebay for cheap, should I worry? is there a certain pitch for M2 and M2.5 for a machine screw?

 

[Cogsy]

As far as I know there is only one thread pitch for M2 and M2.5 but there are massive differences in taps. Differences in design - spiral, taper, bottoming/plug - and different materials, HSS, carbon steel, etc.

Most people will recommend you stay away from cheap taps, especially in the very small sizes. Broken taps in critical holes are no fun at all.

 

[Speedy]

just going to be used in aluminum.
good point on cheap taps, I suppose even in aluminum they can break off.

any input on the reamer? the idea is I have to screw down a bearing cap on a small part, instead of putting dowel pins to locate the two parts I thought since I am doing a bolt circle I can ream the bearing cap tight to the bolts and the housing will take the threads. maybe its overkill and unnecessary because I machined a recess in the bearing cap to sit into the housing so it should be centered.

I would expect that reamer to be expensive to!

is there any take on cheap machine screws from overseas? hardware locally is ridiculous amount of money.. for our models I am wondering if its safe to purchase overseas as quantities seem reasonably priced.

 

[Swifty]

Michael, I think that you will find that the manufacturing tolerances on the screws will not give you a precise size to fit in a reamed hole. I have used screw holes to locate parts for machining, but it's not as accurate as dowel pins.

Paul.

 

[Speedy]

Hi Paul,
I just put down my caliper as I read your post, your correct.
have variance with most of the screws and it looks like it would be troublesome idea.
has any of the membership purchased ebay bulk screws? seems like I can get 100 M2x11mm for $10 should I be afraid of quality?

what would be the proper procedure to instal dowel pins? I think I will also do some research.

here is the part, as you can see both caps have a lip that centers itself in the bore. all done before parting off. next time around I think dowels would need to be drilled before parting off. maybe not? after all I still need to drill the bolt circle.

 

[Swifty]

Hi Michael, if the cap is a neat fit in the bore, then there is no need for dowel pins as well. What is the finished part doing? you refer to it as a bearing cap, is it for a ball race or plain bearing, is the cap going to be bored to insert a bearing?. Sorry for all the questions, but the better idea that we get of the finished article, the better we can advise.

If you still want to put dowels in, just bear in mind that you will need a through hole to knock them out if required, or else they will have to be a sliding fit in blind holes.

Paul.

 

[Wizard69]

just going to be used in aluminum.
good point on cheap taps, I suppose even in aluminum they can break off.

any input on the reamer? the idea is I have to screw down a bearing cap on a small part, instead of putting dowel pins to locate the two parts I thought since I am doing a bolt circle I can ream the bearing cap tight to the bolts and the housing will take the threads. maybe its overkill and unnecessary because I machined a recess in the bearing cap to sit into the housing so it should be centered.

I would expect that reamer to be expensive to!

is there any take on cheap machine screws from overseas? hardware locally is ridiculous amount of money.. for our models I am wondering if its safe to purchase overseas as quantities seem reasonably priced.

As people have already pointed out trying to fit screws to this tolerance would be trying. Many of the screws on the market these days have rolled threads and aren't that accurate for diameter and more importantly runout.

As for screw suppliers I guess it depends upon where you are in the world. Your best bet, if there is a city near by would be to find a fastener supplier to industry. Given a decent supplier the quality would be good but you will have to inspect the product. The reality is that there are many many suppliers of low quality bolts and screws out there. You would also end up buying boxes of 50 or a hundred as most commercial suppliers won't break box sizes. Box sizes aren't as bad as it sounds as the prices seen at home centers are often outrageous. Learn to cut the bolts and one box can be suitable for a number of uses.

Taps come in so many flavors that advice can be hard to give. For example some gunsmiths will suggest carbon taps because a broken tap is easy to smash. I prefer better quality HSS myself. The reality is that you will eventually break a tap, that will lead to a learning experience as getting such small taps out of the hole isn't easy. Such problems are often the reason people build EDM machines.

 

[goldstar31]

Of course Wizard69 is not only only correct but 'more than correct'

My thought are. Why reamers when quite a lot of hand reamers are tapered!
Wouldn't it be easy to use drills- cheap enough in number and letter sizes and usually hss.

Unless you have decent boring and diameter measuring kit, getting cheap jack nuts and bolts is a doubtful business.

My thoughts, of course

Norman

 

[grapegro]

Hello Speedy,
On my current project, I am using many 2, 2.5 and 3mm screws, some in long lengths for their diameter. I have been very successful in finding quality screws from hobby supplies, mainly Hobby King, for very reasonable prices.
Norm Cooper

 

[Jasonb]

You are unlikely to get a good fit with off the shelf screws, bolts will not be a lot better. You need to make "fitted bolts" these will have the plain unthreaded part of the shank turned to a good fit in your reamed hole.

I often make these for conrod caps and eccentric straps.

In your case buy 2.0mm and 2.5mm H7 tollerance reamers, turn your bolts to a good fit in these which will be 2.0mm or 2.5mm or a whisker over and then cut your threads which will if teh die is correctly adjusted be on size or a fraction under so will pass through the reamed hole

 

[bazmak]

Countersunk screws into tapped holes give an accurate location similar to dowel pins.If you mark out and drill/csk the holes,spot thru and drill and tap one hole
then fit one screw.Repeat as necessary for a no of screws.Dont know if you can get csk skt head screws at that size,but as prvios answer if you have a close tolerance spigot and recess you dont need precision screws use hx/soct cap screws which are readily available down to M2

 

[Herbiev]

Are you using metric coarse or metric fine thread. Metric coarse 2mmx 0.4 and 2.5mmx0.45 or fine 2mmx 0.25 and 2.5 mm x 0.35. I often use metric fine but taps and dies are very expensive.

 

[MachineTom]

Let us think about your first question, Reaming thru holes to bolt size, I do not know what sort of equipment you have, so I will assume its a mini mill. If you drilled and reamed 2 holes 25mm apart first the threaded piece, then the thru hole piece with reamed to body size holes, you will likely not be able to bolt them together. On a 8mm in my hand, the diameter at the radius just under the head is 8.23mm yes larger than the shank which has a taper down to 7.70mm, the threaded portion varies from 7.82 to 7.87mm. Though the shank is 7.9mm+ it would be difficult to drill two holes that varied less than .05mm in alignment. Even if you stacked drilled the pieces, you maybe could be able to fit them together.

Doweling is more difficult than bolting if stack drilled for a one position only fit. If you are doing two blind holes or multi position fitting, not much chance without the right equipment and setup.

When I do doweling The DRO is set on .0001" resolution, Parts set with stops , all table feeding from the same direction, Head trammed before starting, drill then ream each hole of one part, then the next part. Not very quickly done.

 

[Speedy]

thank you all for responding!

the part is a housing for a differential and pinion, for my cox inline twin teather car.
the end caps will have bearings, which now I am unsure on how to machine them true to the case.
for the question on dowel pins, I now realize I am not equipped for this so I will just make my bolt circle with socket head screws, it sounds like I made the part correctly to not need dowels.

I dont have the taps yet, but I think I am using coarse thread, I didnt see options for fine thread and seems like those would be more money! M2 is already expensive.

looks like I need to devote a weekend to installing my digital read out on my mill so I can be better equipped for future use.

maybe I can pluck everyones brain on how to machine the bearing caps and set up the pinnion. I am seeing flaws in my design. but might be able to work around them.

 

[Speedy]

this is the housing, the differential is a close tolerance fit in the bore, as you will see I forgot that this would impede on installing the pinion gear for proper gear mesh.

I was going to drill a hole the size of the pinion shaft in the middle of the housing, then insert the pinion in the bore and seat it (roughly shown in second picture)

but shown on the third picture you can see the amount of the bore I would need to remove to make the pinion sit flush in the housing and get a proper gear mesh, the question is how do I go about doing this!.

I am thinking to just machine the diameter of the pinion head out of the axle housing in the lathe, so center the cutter inside the bore and remove the material that represents the diameter of the pinion head, so it can sit further in? does this make sense for the application.

 

[MachineTom]

There are a couple of thoughts that you need to consider with this gearing.
How will adjust backlash.
How will you adjust pinion depth.
How will you support the pinion and its bearings.

If mine, I would make the carrier bearing with threaded plugs. Then bearing end play can be set, and carrier can be shifted for tooth engagement profile.
The pinion mounted in a tube that threads into a blocked welded to the carrier housing.
With the threads. Providing movement to set pinion depth.

 

[Speedy]

There are a couple of thoughts that you need to consider with this gearing.
How will adjust backlash.
How will you adjust pinion depth.
How will you support the pinion and its bearings.

If mine, I would make the carrier bearing with threaded plugs. Then bearing end play can be set, and carrier can be shifted for tooth engagement profile.
The pinion mounted in a tube that threads into a blocked welded to the carrier housing.
With the threads. Providing movement to set pinion depth.

I think I am okay with the differential shimming as I have some shims here.
the pinion is where I am having difficulty, I think I am going to use the tube idea but leaning towards bolting it to the axle housing.

will contemplate your idea, seems like a good one not fond of the welding not set up for aluminum.

 

[Wizard69]

One thing I failed to mention is the use of stripper bolts sometimes called shoulder bolts. While likely not suitable for this use they are useful for assemblies that need to go together often fairly accurately. Often they are far more convenient than dowel pins for reasonably precise assemblies.

 

[Dave Sohlstrom]

I use nuts and bolts from these folks http://rtlfasteners.com/ and these folks
http://www.americanmodeleng.com/index.html

Both have good pricing. I used close to 100 nuts and bolts for this set of engines in a stern wheeler.

https://youtu.be/QEYhOBMRTHU

Dave